The page is mostly verbatum from the article listed below. However, I have redrawn all of the diagrams/tables, added some modifications, and comments. These additions will be ended with my call sign. There is also a section, that I added, at the bottom named MC6800 EPROM Programmer Modifications for Other EProms. That section describes modifying the original EPROM Burner for the other EPROM configurations. - K7MEM

MC6800 EProm Programmer, by Robert Degler, Popular Electronics, August 1980

an EPROM programmer for 6800 computer

Low-cost device program the 1K-by8-bit 2708 EPROM using specially provided software

One of the handiest devices available to the small-computer user is the EPROM (Erasable Programmable Read Only Memory). The basic ROM's advantage over RAM (Randon Access Memory) is that its contents are retained when operation power is removed. This means that often-used programs such as bootstraps, monitors, operating systems, high-level languages, etc., can be permanently stored, thus eliminating time-consuming data retrieval from cassette or paper tape.

An EPROM is a special type of ROM that can be erased, and re-programmed as desired. Consequently, it makes an ideal storage medium for semipermanent data for experimental programs, or for software prototyping where changes may be made as work progresses.

The EPROM Programmer described here is an inexpensive device that can program the popular 1K by 8-bit, low cost 2708 EPROM when used with a 6800-based computer having an MC6820 PIA (Peripheral Interface Adapter). The simple schematic on the next page illustrates this.

The computer, controlled by software to be described, supplies the EPROM PRogrammer with correct addresses, data, and properly timed programming pulses. In addition, the software ensures that the EPROM contains after programming is correct. The software also transfers the entire contents, or any portion of it, into RAM (where it can be altered) and writes it into blank EPROM or returns it to the same one. The software package is positione-independent and occupies less than 256 bytes.

Circuit Operation

As shown in the schematic, lines PB0 through PB7 of the B side of the PIA supply the necessary addresses to the EPROM. Quad latch IC1, strobed by control line CB2, latches the two most significant address lines (A8 and A9) to the EPROM to form the required 10-bit address (2¹⁰ = 1024)

When switch S1 is placed in the READ position, pin 20 (Chip Select) of the EPROM is grounded and power is removed from the transistor circuit driving tthe PROG input (pin 18). The computer can now examine the contents of the EPROM. In this mode, lines PA0 through PA7 of the A side of the PIA allow the EPROM data to reach the computer

In the PROGRAM setting of S1 pin 20 (Write Enable) of the EPROM is connectes to +12 volts to place the EPROM in its programming mode. Lines PA0 through PA7 now allow the computer to supply data to the EPROM. The other section of S1 connects +26 volts to the three-transistor circuit that generates the programming pulse for pin 18. Transistors Q2 and Q3 form a complementary pair that actively pulls the programming input high or low as recommended by the 2708 data sheets. The when-to-burn signal comes in via CA2.

Software

This consists of four major sections; VBLNK, READ, BURN, VRFY and several subroutines.Although the order of these routines may appear strange, they are carefullly arranged so that all internal branching may be in the relative mode. This allows the code to be executed at any address in the system memory without change.

Subroutine INIT initializes the PIA so that the A-lines are inputs, the B-lines are outputs with CA2 high and CB2 low. This subroutine also disables the IRQ level interrupts so that nothing will disturb the timing of the programming pulses, and because memory locations $A000 and $A001, use to store the IRQ interrupt vector by JBUG and MIKBUG, are used here to store PRMAD (starting EPROM address set by user). This routine is also called at the beginning of each of the four other major sections of the software.

Subroutine ADROUT is used to output the 10-bit address for the EPROM. The most significant two bits are output on the PIA B-side followed by raising and lowering CB2 to latch these two bits into IC1. The least-significant bits are then output, which together with the first two bits, make up the required 10-bit address. The EPROM address (PRMAT) is then incremented in the computer's RAM

Subroutine INPUT calls subroutine ADROUT to output the current address to the EPROM and then loads Accumulator-A with the contents of this location of the EPROM.

Subroutine VERI calls subroutine INPUT to get a byte of information from the EPROM. It then compares this byte with the contents of Accumulator-B. If they are the same, it returns to the caller. If an error is detected, the index register is decremented so that it will point to the failing EPROM address. A software interrupt is then executed to return to the monitor. Accumulator-A will contain the bad data, and Accumulator-B the expected data.

Subroutine WRITE is used to generate the correct width programming pulses for pin 18 of the EPROM. See the description of the BURN routine below for details of this pulse.

Program section VBLNK makes sure that the EPROM is erased before attempting to progran it. Each byte in the EPROM is compared with $FF, which is the erased state It is not necessary to start verifying the EPROM address 0000. If a section of the EPROM already contains data, and it is desired to verify that the rest of the EPROM is blank so that additional data can be inserted, then the desired start of verification address is placed in memory location PRMAD and PRMAD+1. Otherwise these two locations should be set equal to zero prior to starting execution at locations VBLNK

The READ section is used to transfer the contents of the EPROM into the computer's RAM. Anything from 1 byte to the entire 1024 bytes may be transferred by setting up PRMAD, BEGAD, and ENDAD prior to execution. Keep in mind that PRMAD is the location within the EPROM and has nothing to do with the memory address at which the EPROM will be located when installed in the system. PRMAD equal to zero implies the first location within the EPROM. Data is transferred from the EPROM starting at location PRMAD into RAM addresses BEGAD through ENDAD inclusive.

Section VRFY compares the data contained in RAM addresses BEGAD through ENDAD with the data stored in the EPROM starting at location PRMAD. If an discrepencies are found, a software interrupt (SWI) is issued to return to the monitor. With most 6800 monitors, this will cause a display of the CPU registers. At this time, the Index Register will contain the location within the EPROM that contains the failing data, Accumulator-A will contain the failing data, and Accumulator-B will contain what the data should have been.

A BURN routine "burns" the data into the EPROM. Once the EPROM has been put in the PROGRAM mode via S1, the address and data to be programmed into that address are applied to the EPROM. Then a +26 volt program pulse is applied to pin 18. Duration of the pulse must be at least 100µs and not more than 1 ms. The next address and corresponding data are applied and another programming pulse is issued. This continues until all the addresses have been programmed. The entire process is repeated 256 times. This is done because the total program time applied to each address must be greater than, or equal to, 100ms. As it is forbidden to apply more than one pulse at a time to any address, programming of the sequential addresses must be repeated many times.

THe system that this is currently being used one is an MEK6800D2, a Motorola two-board microcomputer kit, that runs at a clock rate of 614.4 KHz. The number 36₁₀ (25₁₆) loaded into the INDEX register in the WRITE subroutine is used to establish the width of the program pulse. If a clock rate of 1 MHz is used, this number should be changed to 61₁₀ (3D₁₆). This is based on eight machine cycles in the two-instruction loop at label WRT1, and an additional eight machine cycles outside this loop. If the duration of the program pulse is maintained at 500 µs and the program loop is repeated 256 times, this allows a total program time of 128 ms/location.

Data sheets for the 2708 specify that all 1024 locations should be programmed in each loop, but making the loop as small as 128 bytes has proved successfu. Making the loop too small may be detrimental to to the EPROM. Length of the program loop is estblished as ENDAD-BEGAD+1. Note that, at 614.4 KHz, the time required to program all 1024 bytes is only about two and a half minutes.

MC6800 CROSS ASSEMBLER eprom_gen.src Sun, Nov 18, 2018 15:34:04 LINE ADDR OP OPER LABEL OPCODE OPERAND 00010 0000 OPT RELOC,LINENUM=10,LINEINC=10 00020 0000 NAME PUP 00030 * OPT LLEN=120,PAGE=77,SEQ,CREF 00040 * 00050 ********************************************************************* 00060 * 00070 * PROM UTILITY PROGRAM 00080 * VERSION 1.2 00090 * JAN. 25, 1979 ROGER DEGLER 00100 * 00110 * NOTE: THIS CODE IS POSITION INDEPENDENT. 00120 * IT MAY BE EXECUTED AT ANY ADDRESS WITHOUT CHANGES. 00130 * 00140 * START EXECUTION AT: 00150 * VBLNK = VERIFY BLANK EPROM 00160 * READ = MOVE CONTENTS OF EPROM INTO RAM 00170 * BURN = PROGRAM THE EPROM 00180 * VRFY = VERIFY CONTENTS OF EPROM AFTER PROGRAMMING 00190 * 00200 ********************************************************************* 00210 * 00220 C000 ORG $C000 SET STARTING ADDRESS TO HEX C000 00230 8004 PAD EQU $8004 PIA "A" SIDE DATA REG. 00240 8005 PAC EQU PAD+1 PIA "A" SIDE CONTROL REG. 00250 8006 PBD EQU PAD+2 PIA "B" SIDE DATA REG. 00260 8007 PBC EQU PAD+3 PIA "B" SIDE CONTROL REG. 00270 * 00280 E08D JBUG EQU $E08D START ADDRESS OF MONITOR 00290 * 00300 ** THE THREE FOLLOWING 16-BIT VALUES MUST BE SET UP 00310 ** BY THE USER BEFORE BEGINNING PROGRAM EXECUTION 00320 * 00330 A000 PRMAD EQU $A000 STARTING EPROM ADDRESS -- SET BY USER 00340 A002 BEGAD EQU PRMAD+2 STARTING MEMORY ADDRESS -- SET BY USER 00350 A004 ENDAD EQU PRMAD+4 ENDING MEMORY ADDRESS -- SET BY USER 00360 * 00370 A032 PRMAT EQU $A032 EPROM ADDRESS FOR SOFTWARE -- DOESN'T CHANGE PRMAD 00380 A034 MEMAD EQU PRMAT+2 START MEMORY ADDRESS FOR SOFTWARE -- SAVES BEGAD 00390 * 00400 * THE TWO PREVIOUS VARIABLES ARE USED BY THE SOFTWARE 00410 * SO THAT THE USER DEFINED VARIABLES PRMAD AND BEGAD 00420 * WILL NOT BE ALTERED BY EXECUTION OF THE PROGRAM 00430 * 00440 A036 BRNCTR EQU MEMAD+2 COUNTER USED TO COUNT PROGRAMMING PASSES 00450 * THROUGH THE EPROM 00460 * 00470 ********************************************************************* 00480 * 00490 * HERE ARE THE ENTRY POINTS 00500 * 00510 C000 20 06 VBLNK BRA VB0 VERIFY BLANK EPROM 00520 C002 20 11 READ BRA RD0 TRANSFER EPROM TO RAM 00530 C004 20 6B BURN BRA BRN0 PROGRAM THE EPROM 00540 C006 20 54 VRFY BRA VFYL VERIFY CONTENTS OF EPROM 00550 * 00560 ********************************************************************* 00570 * 00580 * THIS SECTION VERIFYS EPROM BLANK 00590 * 00600 ********************************************************************* 00610 * 00620 C008 8D 22 VB0 BSR INIT INITIALIZE PIA FOR READ OPERATION 00630 C00A C6 FF LDAB #$FF CHECK CONTENTS OF EPROM FOR ALL ONES 00640 C00C 8D 3D VLP BSR VERI GET EPROM DATA AND CHECK IT 00650 C00E 8C 0400 CPX #$0400 DONE CHECKING ENTIRE EPROM YET? 00660 C011 26 F9 BNE VLP BRANCH IF NO 00670 C013 20 44 BRA JJBG RETURN TO MONITOR 00680 * 00690 ********************************************************************* 00700 * 00710 * THIS SECTION XFERS CONTENTS OF EPROM INTO RAM 00720 * 00730 ********************************************************************* 00740 * 00750 C015 8D 15 RD0 BSR INIT INITIALIZE PIA FOR READ OPERATION 00760 C017 FE A0 02 LDX BEGAD SET UP STARTING MEMORY ADDRESS 00770 C01A FF A0 34 RD1 STX MEMAD 00780 C01D 8D 34 BSR INPUT GET DATA FROM EPROM 00790 C01F FE A0 34 LDX MEMAD GET MEM. ADR 00800 C022 A7 00 STAA 0,X PUT EPROM DATA INTO MEMORY 00810 C024 BC A0 04 CPX ENDAD DONE? 00820 C027 27 30 BEQ JJBG JUMP TO MONITOR IF YES 00830 C029 08 INX INC MEM. ADR IF NOT 00840 C02A 20 EE BRA RD1 00850 * 00860 ********************************************************************* 00870 * 00880 * SUBROUTINE TO INITIALIZE PIA 00890 * 00900 ********************************************************************* 00910 * 00920 C02C 0F INIT SEI DISABLE IRQ INTERUPTS 00930 C02D CE 8004 LDX #PAD POINT X TO PIA 00940 C030 86 38 LDAA #$38 INITIALIZE PIA 00950 C032 A7 01 STAA 1,X OBTAIN ACCESS TO A SIDE DDR 00960 C034 A7 03 STAA 3,X OBTAIN ACCESS TO B SIDE DDR 00970 C036 6F 00 CLR 0,X SET A SIDE AS OUTPUTS 00980 C038 6F 02 CLR 2,X 00990 C03A 6A 02 DEC 2,X SET B SIDE AS OUTPUTS 01000 C03C 86 3C LDAA #$3C OBTAIN ACCESS TO B SIDE DATA REG. 01010 C03E A7 01 STAA 1,X 01020 C040 86 34 LDAA #$34 01030 C042 A7 03 STAA 3,X OBTAIN ACCESS TO B SIDE DATA REG. 01040 C044 FE A0 00 LDX PRMAD SET PRMAT = PRMAD TO PROTECT PRMAD 01050 C047 FF A0 00 STX PRMAD 01060 C04A 39 RTS 01070 * 01080 ********************************************************************* 01090 * 01100 * SUBROUTINE TO COMPARE ONE BYTE OF EROM DATA WITH 01110 * ONE BYTE OF RAM DATA. 01120 * 01130 ********************************************************************* 01140 * 01150 C04B 8D 06 VERI BSR INPUT GO GET DATA FROM EPROM 01160 C04D 11 CBA COMPARE IT WITH ACCUMULATOR-B 01170 C04E 27 02 BEQ VRT BRANCH IF COMPARISON IS OK 01180 C050 09 DEX DECREMENT EPROM ADR SO IT WILL POINT TO FAILING ADR. 01190 C051 3F SWI SOFTWARE INTERRUPT -- THIS IS AN ERROR RETURN 01200 * UPON THIS RETURN: 01210 * X = EPROM ADR. 01220 * A = DATA FROM EPROM (BAD) 01230 * B = EXPECTED DATA 01240 * 01250 C052 39 VRT RTS 01260 * 01270 ********************************************************************* 01280 * 01290 * SUBROUTINE TO READ ONE BYTE OF DATA FROM EPROM 01300 * 01310 ********************************************************************* 01320 * 01330 C053 8D 75 INPUT BSR ADROUT GO OUTPUT EPROM ADDR TO EPROM 01340 C055 B6 80 04 LDAA PAD READ CONTENTS OF EPROM -- PUT IN ACC-A 01350 C058 39 RTS 01360 * 01370 ********************************************************************* 01380 * 01390 * EXIT TO MONITOR -- USE START ADDRESS OF MONITOR 01400 * FOR TYPE OF SYSTEM INSTALLED ON. 01410 * 01420 ********************************************************************* 01430 * 01440 C059 7E E0 8D JJBG JMP JBUG THIS IS THE ONLY NORMAL RETURN TO MONITOR 01450 * 01460 C05C 20 4F VFYL BRA VFY0 THIS IS A LINK TO THE VERIFY SUBROUTINE. 01470 C05E 20 CC INITL BRA INIT THIS IS A LINK TO THE INIT SUBROUTINE. 01480 * 01490 ********************************************************************* 01500 * 01510 * SUBROUTINE TO ISSUE THE PROGRAM PULSE 01520 * 01530 ********************************************************************* 01540 * 01550 C060 86 34 WRITE LDAA #$34 ISSUE PROGRAM PULSE 01560 C062 B7 80 05 STAA PAC TURN PULSE ON 01570 C065 CE 0025 LDX #37 DELAY 500 USEC (37 IS FOR 616.4 KNZ CLOCK) 01580 C068 09 WRT1 DEX STAY IN THIS LOOP UNTIL X = O 01590 C069 26 FD BNE WRT1 BRANCH IF NOT DONE YET 01600 C06B 86 3C LDAA #$3C TIME IS UP -- CLR PROGRAM PULSE 01610 C06D B7 80 05 STAA PAC 01620 C070 39 RTS 01630 * 01640 ********************************************************************* 01650 * 01660 * THIS IS THE SECTION TO PROGRAM THE EPROM. 01670 * 01680 ********************************************************************* 01690 * 01700 C071 8D B9 BRN0 BSR INIT GO INIT PIA FOR READ OPERATION 01710 C073 86 38 LDAA #$38 CHANGE PIA SO A SIDE = OUTPUTS 01720 C075 B7 80 05 STAA PAC 01730 C078 7A 80 04 DEC PAD 01740 C07B 86 3C LDAA #$3C 01750 C07D B7 80 05 STAA PAC 01760 * 01770 C080 7F A0 36 CLR BRNCTR CLR THE LOOP COUTER -- WE ARE GOINT TO DO 256 LOOPS 01780 * 01790 C083 FE A0 00 BRN1 LDX PRMAD SET PRMAT = PRMAD TO SAVE PRMAD 01800 C086 FF A0 32 STX PRMAT 01810 C089 FE A0 02 LDX BEGAD SET MEMAD = BEGAD TO SAVE BEGAD 01820 C08C FF A0 34 BRN2 STX MEMAD 01830 C08F 8D 39 BSR ADROUT OUTPUT EPROM ADR TO EPROM (ADROUT INCS PRMAT) 01840 C091 FE A0 34 LDX MEMAD GET MEM ADR 01850 C094 A6 00 LDAA 0,X GET DATA FROM MEMORY 01860 C096 B7 80 04 STAA PAD OUTPUT DATA TO EPROM 01870 C099 8D C5 BSR WRITE GO ISSUE 500 USEC PROGRM PULSE 01880 C09B FE A0 34 LDX MEMAD GET MEM ADR 01890 C09E BC A0 04 CPX ENDAD HAVE WE DONE ALL MEMORY ADRS. YET? 01900 C0A1 27 03 BEQ BRN3 BRANCH IF YES 01910 C0A3 08 INX IF NOT THEN INCREMENT MEM ADR 01920 C0A4 20 E6 BRA BRN2 AND GO BURN NEXT ADR 01930 * 01940 C0A6 7C A0 36 BRN3 INC BRNCTR INCREMENT THE LOOP COUNTER 01950 * WHEN BRNCTR = 0 THEN WE HAVE BURNEDEACH 01960 * ADDRESS 256 TIMES AND ARE DONE. 01970 C0A9 26 D8 BNE BRN1 IF NOT DONE GO TO BEGINNING AND BURN ALL ADDRS. AGAIN 01980 C0AB 20 AC BRA JJBG IF WE ARE DONE THEN RETURN TO THE MONITOR 01990 * 02000 ********************************************************************* 02010 * 02020 * THIS IS THE SECTION TO VERIFY THE CONTENTS OF THE 02030 * EPROM ARE THE SAME AS THE CONTENTS OF RAM. 02040 * 02050 ********************************************************************* 02060 * 02070 C0AD 8D AF VFY0 BSR INITL INIT PIA FOR READ OPERATION 02080 C0AF FE A0 00 LDX PRMAD SET PRMAT - PRMAD TO SAVE PRMAD 02090 C0B2 FF A0 32 STX PRMAT 02100 C0B5 FE A0 02 LDX BEGAD SET MEMAD - PEGAD TO SAVE BEGAD 02110 C0B8 FF A0 34 VFY1 STX MEMAD 02120 C0BB E6 00 LDAB 0,X GET DATA FROM MEMORY 02130 C0BD 8D 8C BSR VERI GO COMPARE WITH DATA FROM EPROM 02140 C0BF FE A0 34 LDX MEMAD WE RETURNED IF EPROM DATA WAS OK 02150 C0C2 BC A0 04 CPX ENDAD ARE WE DONE CHECKING ALL ADRS? 02160 C0C5 27 92 BEQ JJBG RETURN TO MONITOR IF YES 02170 C0C7 08 INX IF NOT THEN INC MEM ADR 02180 C0C8 20 EE BRA VFY1 AND CONTINUE CHECKING. 02190 * 02200 ********************************************************************* 02210 * 02220 * SUBROUTINE TO OUTPUT ADDRESS TO EPROM 02230 * 02240 ********************************************************************* 02250 * 02260 C0CA CE 8004 ADROUT LDX #PAD POINT X TO PIA 02270 C0CD B6 A0 32 LDAA PRMAT GET MOST SIGNIFCANT BYTE OF EPROM ADR 02280 C0D0 A7 02 STAA 2,X OTUPUT IT TO THE LATCH (IC1) 02290 C0D2 86 3C LDAA #$3C STROBE THE ADR LATCH 02300 C0D4 A7 03 STAA 3,X 02310 C0D6 86 22 LDAA #34 CLEAR THE STROBE 02320 C0D8 A7 03 STAA 3,X 02330 C0DA B6 A0 33 LDAA PRMAT+1 GET LEAST SIG. BYTE OF EPROM ADR 02340 C0DD A7 02 STAA 2,X OUTPUT IT 02350 C0DF FE A0 32 LDX PRMAT GET ENTIRE EPROM ADR 02360 C0E2 08 INX INCREMENT IT 02370 C0E3 FF A0 32 STX PRMAT AND PUT IT BACK 02380 C0E6 39 RTS 02390 * END ------------------------------ Assembly Errors ------------------------------ ------------------------------- Symbol Table ------------------------------- -------------------------------------------------------------------------- | Symbol - Value | Symbol - Value | Symbol - Value | |------------------------+-------------------------+------------------------| | ADROUT - $C0CA | JBUG - $E08D | VB0 - $C008 | | BEGAD - $A002 | JJBG - $C059 | VBLNK - $C000 | | BRN0 - $C071 | MEMAD - $A034 | VERI - $C04B | | BRN1 - $C083 | PAC - $8005 | VFY0 - $C0AD | | BRN2 - $C08C | PAD - $8004 | VFY1 - $C0B8 | | BRN3 - $C0A6 | PBC - $8007 | VFYL - $C05C | | BRNCTR - $A036 | PBD - $8006 | VLP - $C00C | | BURN - $C004 | PRMAD - $A000 | VRFY - $C006 | | ENDAD - $A004 | PRMAT - $A032 | VRT - $C052 | | INIT - $C02C | RD0 - $C015 | WRITE - $C060 | | INITL - $C05E | RD1 - $C01A | WRT1 - $C068 | | INPUT - $C053 | READ - $C002 | - $0 | ---------------------------------------------------------------------------

Construction

Since the circuit is not critical, the Programmer can be built using perf board with Wire-Wrap techniques, or a small pc board can be designed. To avoid pin damage, the use of a low-insertion force socke for the EPROM is suggested. Sockets for IC1 and the three transistors are optional.

Suitable connectors must be made to contact the A and B parts of the MC6820 PIA and the CA2 and CB2 lines. Sources of +5, -5, +12 and +26 volts are also needed.

Any type of enclosure can be used as long as it will hole the power supplies with EPROM socket and S1 on top.

Use

Switch S1 should be in the READ position whenever an EPROM is inserted in or removed from the socket. In its unprogrammedd state, the EPROM contins logic 1's at all storage locations. These 1's may be changed to 0's by programming - but 0's may be changed to 1's only by erasing the entire EPROM with exposure to 2537-Angstrom ultra violet light.

Programming can, in certain cases, alter the contents of a previously programmed EPROM. For example, 27₁₀ (0010 0111₂) can be changed to 23₁₀ (0010 0011₂), but not vice versa. This is accomplished by using the READ routine to transfer the contents of the EPROM into RAM, locating the 27₁₀ in the RAM, changing it to 23₁₀, then using BURN to program this data back into the same EPROM.

To program in a small section of new data, for example only four bytes, use VBLNK to make sure that the four locations are in the unprogrammed state. THen with the EPROM removed from the socket, use READ to initialize a section of RAM to all 1's. This can be done because data read back from an empty socket is FF₁₆.

Place the four data bytes in the RAM buffer, replae the EPROM and use S1 at PROGRAM and BURN to program the data into the EPROM. Keep this section at least 128 bytes long. Since trying to program a 1 nto the EPROM has no effect, only the four bytes of new data will make a change in the EPROM contents. After using BURN, set S1 to READ and use VRFY subroutine to make sure that the EPROM was correctly programmed.

Once you gain some proficiency in programming, you can create "personality modues" for any function you desire, from instant bootstrap at turn-on, to full BASIC at the touch of a key.

MC6800 EProm Programmer Modifications for Other EProms

I'm including this sections because, I don't have any 2708s. But I do have a bunch of EPROMS with different configurations and different programming requirements. I have 34-Intersil IM5654 (512 x 8), and 4-Hitachi HN27C64G-20 (8K x 8). I like the overall approach of the programmer, but it needs to be modified, hardware and software, to make it useful with the EPROMs that I have.

Modification for those two EPROMs shold make the programmer a bit simpler, as the two EPROMs that I have only require +5 Volts, for normal operation. Unlike the 2708 which requires +5V, -5V, & +12Volts.

It should be noted that, if your intent is to use 2716, there is a bit of a hitch that you need to be aware of. Both Texas Instrument (TI) and Intel developed EPROMs at the same time. During the development of TI's TMS-2716, TI followed the same format as the TMS-2708, with the requirements for multiple supply voltages (+5V, -5V, & +12V). However, before TI could release their TMS-2716 EPROM, Intel released their version of the 2716 that only required a single 5 Volt power supply, for normal operation. TI then changed the designator to TMS-2516 to make sure the user didn't mix it with the 2716s.
TMS-2516 is equivalent to the Intel (and all other) 2716s
TMS-2716 is NOT equivalent to other 2716s TI specific, limited use (..in arcade games anyways..) bigger and bigger 27XX series EPROMs, Texas Instruments created a 25XX series. While most of the EPROMs were equivalent (2732 is equivalent to 2532) the 2716 was not equivalent to the TI 2516

The drawing on the right shows the two EPROMs, schematically. Overall, the two EPROMs are very similar. Probably the most notable difference is in the Power Requirements. The M2708 requires +5, -5, and +12 volts. Wheras, the M2716 only requires +5 volts. Of course, they both require +26 volts during programming. The table below illustrates the similarities and differences.

	M2708	IM5654	HN27C64G
Package	24 Pin Dip	24 Pin Dip	28 Pin Dip
Format	1,024 x 8	512 x 8	8,192 x 8
Power Req	+5, -5, and +12 volts	+5 volts	+5 volts
Programming Voltage	+26 volts	+26 volts	+26 volts
Data Width (D)	8 Bits - D0-D7	8-Bits - D0-D7	8-Bits - D0-D7
Address Width (A)	10 Bits - A0-A9	9-Bits - A0-A8	13-Bits - A0-A12
Read Enable	20-CS/WE	20-E1, 22-E2, 21-S	20-CE, 22-OE
Program Enable	18-Prog	18-Pgm	27-PGM

DEVICE OPERATION - The M2716 has 3 modes of operation in the normal system environment. These are shown in Table 3.

Read - For both of the EPROMs the read operation is very similar. As long as the basic power requirements are supplied (+5V, -5V, +12V - M2708 or +5V -M2716), the Read Enable pins (20-CS/WE - M2708 or 20-G - M2716) can be used to enable the read mode. TheM2716 has 3modes of operation in the normal system environment. These are shown in Table 3.

Programming - To burn the 2708 EPROM we need to power them as follow: -5V to the VBB pin (21), +12 V to the VDD (19) and the Not Chip Select pin (20), +5V to the VCC pin (24) and set the VSS pin (12) to ground; we also need to initially put the programming pin (18) to ground. At this point we have to simply write on the address bus (A0…A9) the address of the location to program, in the data bus (Q0….Q7) the data to be written, and set the programming pin (18) to +26 V to program it. We need to wait the correct time for the data to be burned (about 1 ms according to the datasheet) and put back to ground the programming pin (18).

We are in the process of creating the burning part needed in our circuit board, the PIC software and the corrispondent burning utility in Python. This is not a difficult task, but now we don’t need it in a hurry because, in case of necessity, we can simply change a 2704 or a 2708 with a 2716 or a 2732, just programming their first 512 or 1024 bytes, because those EPROM are pin to pin compatible.

DEVICE OPERATION - TheM2716 has 3modes of operation in the normal system environment. These are shown in Table 3.

Read Mode - The M2716 read operation requires that G = VIL, EP = VIL and that addresses A0-A10 have been stabilized. Valid data will appear on the output pins after time tAVQV, tGLQV or tELQV (see Switching Time Waveforms) depending on which is limiting.

Deselect Mode - The M2716 is deselected by making G = VIH. This mode is independent of EP and the condition of the addresses. The outputs are Hi-Z when G=VIH . This allows a Wired-OR of 2 or more M2716’s for memory expansion.

Standby Mode (Power Down) - The M2716 may be powered down to the standby mode by making EP = VIH. This is independent of G and automatically puts the outputs in the Hi-Z state. The power is reduced to 25% (132 mW max) of the normal operating power. VCC and VPP must be maintained at 5V. Access time at power up remains either tAVQV or tELQV (see Switching Time Waveforms).

Programming - The M2716 is shipped from SGS-THOMSON completely erased. All bits will be at “1” level (output high) in this initial state and after any full erasure. Table 3 shows the 3 programming modes.

Program Mode - The M2716 is programmed by introducing “0”s into the desired locations. This is done 8 bits (a byte) at a time. Any individual address, sequential addresses, or addresses chosen at random may be programmed. Any or all of the 8 bits associated with an address location may be programmed with a single program pulse applied to the EP pin. All input voltage levels including the program pulse on chip enable are TTL compatible.

The programming sequence is: with VPP = 25V, VCC = 5V, G = VIH and EP = VIL, an address is selected and the desired data word is applied to the output pins (VIL = “0” and VIH = ”1” for both address and data). After the address and data signals are stable the program pin is pulsed from VIL to VIH with a pulse width between 45ms and 55ms. Multiple pulses are not needed but will not cause device damage. No pins should be left open. A high level (VIH or higher) must not be maintained longer than tPHPL (max) on the program pin during programming. M2716’s may be programmed in parallel in this mode.

Program Verify Mode - The programming of the M2716 may be verified either one byte at a time during the programming (as shown in Figure 6) or by reading all of the bytes out at the end of the programming sequence. This can be done with VPP = 25V or 5V in either case. VPP must be at 5V for all operating modes and can be maintained at 25V for all programming modes.

Program Inhibit Mode - The program inhibit mode allows several M2716’s to be programmed simultaneously with different data for each one by controlling which ones receive the program pulse. All similar inputs of the M2716 may be paralleled. Pulsing the program pin (from VIL to VIH) will program a unit while inhibiting the program pulse to a unit will keep it from being programmed and keeping G = VIH will put its outputs in the Hi-Z state.