Eprom Programmer Mark 1

U1 is the serial line driver/receiver, which converts RS232 standard serial signals to/from standard 5V TTL levels. This IC contains voltage convertors to produce the required transmission voltages (+/- 9V) from a single +5V supply.

In this application the 8 bit received data is used as 4 data bits on R0-R3 and 4 control bits on R4-R7. 3 of these control lines (R4-R6) are taken to a "3 To 8 Line Decoder", U5. The STROBE signal is taken to one of the Enable lines on U5, thereby causing the outputs from this IC to be short pulses. For example, if 00h is received, lines R4-R6 will be low, STROBE will pulse high and consequently pin 15 of U5 will pulse high and the remaining outputs will stay low.

The remaining control bit (R7) controls the power to the EPROM, when it is high all power is removed from the EPROM socket so the device can be inserted or removed. When the device is being read or programmed this line is taken low.

The 4 data lines are taken to the inputs of 4 "Quad D-Type Latches", U6-U9. The Latch Enable lines on these IC's are connected to 4 of the outputs of U5 (Y0-Y3). Data can therefore be stored in these latches by sending the required data on lines R0-R3 and the latch number (0-3) on lines R4-R6. The data will be continuously available on the latch output lines. Referring back to the previous example, if 00h is received, lines R0-R3 will all be low, and line Y0 will pulse high, storing 0h (0000b) in U6. Similarly sending 35h will store 5h (0101b) in U9

Latch U6 is used to hold the least significant nibble (4 bits - half a byte) of the data which will ultimately be programmed into the EPROM, whilst U7 holds the most significant nibble. U8 holds the EPROM type information (see later), and U9 holds 4 setup bits. Bit 1 of U9 controls whether the unit is in Read or Write (Program) mode, bit 2 sets the programming pulse length to either 1 or 40 milliseconds, bit 3 sets the programming voltage to either 12 or 21 volts, and bit 4 sets the supply voltage whilst programming to either 5 or 6 volts. Note that the latches have active-high and active-low outputs, and one or both may be used.

The data outputs from U6 and U7 are taken to a tri-state buffer (U10), which in turn drives the EPROM data lines. U10 is controlled by the R/W- line, such that it's outputs are enabled in Program mode and tri-state in Read mode.

The EPROM data lines are also connected to the data input lines on the UART (U3), and the Y7 output from U5 is connected to pin 23 of U3 (SEND). Therefore if 70h is received, the data currently on the EPROM Data Lines is transmitted back along the serial interface to the computer.

The EPROM Address lines are controlled by counters U11 and U12. These are connected to lines Y4 and Y5 from U5, and are therefore cleared to 0000h by sending 40h and the count is incremented by sending 50h. This approach is quicker than having to send the actual address each time since it only requires one byte to be sent along the serial link.

Line Y6 from U5 (PROG) is used to start a programming pulse. The programming pulse (either 1mS or 40mS) is produced by dividing down the CLOCK2 signal. This signal has a frequency of 19.2KHz (2.4576MHz divided by 128), which equates to a period of 52.1uS. This is fed to counter U13, which is normally held reset by the Set/Reset flip-flop built from U15:C and U15:D. When the PROG line pulses high the flip-flop changes state and the counter starts counting the CLOCK2 pulses. If a 1mS pulse is required, pin 5 of U14:A will be high and pins 12 and 13 of U14:B will be low. When the count reaches 19 (52.1uS x 19 = 989.9uS), all the inputs of U14:A will be high, it's output will therefore go low, changing the state of the flip-flop again, via U16:B, and resetting the counter. A 0.99mS pulse will therefore be present on the output of the flip-flop, 0.99mS being well within the 1mS +/- 5% specification. If a 40mS pulse is required U13 counts 768 CLOCK2 pulses (52.1uS x 768 = 40.01mS).

The PROG PULSE and STROBE signals are coupled via U18:A and U1 to the RS232 CTS (Clear To Send) line. This prevents the host computer from sending further data whilst a program pulse is occurring or while STROBE is still high. This means that data can be sent as fast as possible and no delays are needed in the software.

PROG PULSE- is coupled with the SEND signal to U3 by U16:A. This prevents the SEND signal getting through whilst PROG PULSE- is low. This situation will never occur in normal use, however during initialisation the software requests a 40mS program pulse immediately followed by a SEND. If the RS232 CTS line is present and working then data will be sent, since the CTS line will stop the computer sending the SEND request until after the prog pulse has finished. If CTS is not working the SEND request will be sent immediately but no data will be returned due to U16:A stopping the SEND pulse reaching U3. The software notes the lack of received data, prints a warning and then adds delays itself to allow for the program pulse. You should try to get CTS working properly as there will be a significant speed penalty otherwise.

We now come to the connection switching required for the different EPROM types. The table below shows the pin-outs for the 6 types of EPROM this unit will program. 2716 and 2732 are 24 pin devices and fit into pins 3 to 26 of the EPROM socket, the pin-outs shown below relate to the socket, not the device.

** = No Pin
NC = No Connection
PP+ = Program Pulse, Positive Going
PP- = Program Pulse, Negative Going
OE = Output Enable (Active Low)
CE = Chip Enable (Active Low)
VPP = Programming Voltage
VCC = Supply Voltage
GND = Ground (0V)

It can be seen from the above that most of the pins are the same for all devices. Only 6 pins require special attention, these are 1, 20, 22, 23, 26 and 27, and are marked with a "#" next to the pin number.

The four MODE lines from U9 control the function of these six pins and are set up by the software to suit the EPROM type required. Note that two of the active-low lines are also used. The table below shows the logic levels on each of these lines, for each of the 6 types of EPROM, together with the code that needs to be sent to select that type.

I will now describe what this means for each type of EPROM.

2716:
PIN 1 - not used.

PIN 20 - MODE B and MODE D are both high, so U17:B pin 6 remains high, U16:C pin 8 follows PROG PULSE, as does U17:C pin 8 which is coupled via D6 to PIN 20. PIN 20 is only pulled up in Program mode, so in Read mode it is permanently low.

PIN 22 - MODE A and MODE D are both high, so U15:B pin 6 is low and Q1 and Q2 remain off. R-/W is coupled to the pin via D2.

PIN 23 - MODE D is high, so Q5 and Q6 are on, coupling VPP to PIN 23.

PIN 26 - MODE C is high, so Q7 and Q8 are on, coupling V+ to PIN 26.

PIN 27 - not used.

2732:
PIN 1 - not used.

PIN 20 - MODE B and MODE D are both low. U16:C pin 8 will remain low and U17:B pin 6 will follow PROG PULSE. U17:C pin 8 will therefore be PROG PULSE inverted, and is coupled via D6 to PIN 20. PIN 20 is only pulled up in Program mode, so in Read mode it is permanently low.

PIN 22 - MODE D and MODE C- are both low and MODE A is high, so U15:B pin 6 is high. This switches on Q1 and Q2, coupling VPP to PIN 22

PIN 23 - MODE D is low, so Q5 and Q6 remain off. A11 is coupled to PIN 23 via D4.

PIN 26 - as 2716.

PIN 27 - not used.

2764 and 27128:
PIN 1 - MODE A is high. This switches on Q3 and Q4, coupling VPP to PIN 1.

PIN 20 - MODE B is high and MODE C is low. U16:C pin 8 remains low and U17:B pin 6 remains high, therefore

U17:C pin 8 remains low.

PIN 22 - MODE A and MODE C- are both high, so U15:B pin 6 is low and Q1 and Q2 remain off. R-/W is coupled to PIN 22 by D2.

PIN 23 - as 2732.

PIN 26 - MODE C is low so Q7 and Q8 remain off. A13 is coupled to PIN 26 by D5. Note that in a 2764 EPROM there is no connection to PIN 26.

PIN 27 - MODE B is high and A14 will remain low since it is outside the addressing range. U17:D pin 11 will therefore follow PROG PULSE-.

27256:
PIN 1 - as 2764.

PIN 20 - as 2732.

PIN 22 - as 2764.

PIN 23 - as 2732.

PIN 26 - as 2764.

PIN 27 - MODE B is low so U16:D pin 11 will remain low. U17:D pin 11 will follow A14.

27512:
PIN 1 - MODE A is low so Q3 and Q4 will remain off. A15 is coupled to PIN 1 by D3.

PIN 20 - as 2732.

PIN 22 - MODE A is low so U15:B pin 6 will be high, switching on Q1 and Q2, coupling VPP to PIN 22.

PIN 23 - as 2732.

PIN 26 - as 2764.

PIN 27 - as 27256.

Note that D6 and D7 are germanium types, since silicon types would cause the logic 0 inputs to the EPROM to be at the limit of the specifications.

The two logic gates which would otherwise be unused, are used to control Read and Program LED's. U18:B pin 6 goes low when R-/W and ON-/OFF are both low, lighting D9 (Read) via Q10, whilst U18:C pin 8 goes low when R/W- and ON-/OFF are low, lighting D8 (Program) via Q9. When both LED's are off it is safe to fit or remove the EPROM, the other lines would have been set low by the software before taking ON-/OFF high.

U21 is the main 5 Volt regulator and powers all the logic IC's. D11 protects the whole circuit against reverse polarity, since it is easily possible to reverse the polarity on the sort of PSU used. LED D10 indicates that the unit is powered up.

U20 supplies the power to the EPROM, and is enabled by the ON/OFF- line via Q17 and Q18. Q19 raises the GND pin of U20 by 1 Volt, giving 6 Volts. When 5 Volts is required Q19 is shorted out by Q20 controlled by U18:D, this happens when 5V/6V- or R/W- is low.

U19 is a step-up switching regulator which produces the programming voltage required. The voltage is set by shorting out sections of the resistor chain with transistors. 2716 EPROMs require 25 Volts, not 21 Volts, so the MODE D- line is used to set this. The R-/W line controls Q15 and Q16 which connect the power to the EPROM when the unit is in Program mode.

Type "0F" and check pins 9, 10, 15 and 16 of U6, they should all be at logic 1. Now type "00" and they should all be at logic 0. Typing "05" should give 0101 and "0A" should give 1010. Now repeat the above, replacing the first character with a "1" and checking the levels on U7, then "2" and U8, and finally "3" and U9.

Now type "00", "10", "30" then "70". After you typed the "70" the screen should show "00", the others should have given "**". The "Program" (red) LED should also be on. This set "00" on the data bus, selected write mode to enable U10, then read the data back down the RS232 link. The most likely cause of problems here is the RS232 link again.

Now type "31" then "70". The screen should show "FF" and the "Read" (yellow) LED should be on. U10 is now disabled so it's outputs are tristate and pulled up by RN1.

Typing "30" then "70" should return "00" again. Typing "0F", "1F" then "70" should return "FF", typing "05", "15" then "70" should give "55", and typing "0A", "1A" then "70" should give "AA". Also check that the appropriate data is actually reaching the EPROM socket pins as shown below:

Now we come to the address bus. Type in the program given in Listing 2 (save the other program first as it will be needed again). The program configures the programmer for 27512 EPROM's so all 16 address lines are bought to the EPROM socket and should be checked there. The program clears the address counter and then repeatedly increments the count, pausing at selected points to enable the checks to be made (see Table).

The logic levels should be checked on the pins of the EPROM socket when the program pauses, if a level is incorrect check on the appropriate pin on U11 or U12, then trace the fault as necessary. Note that the program may run quite slowly. A complied version (TEST2.EXE) which runs considerably faster is on the disk available from the author.

Now re-load the first test program. Connect a 'scope or logic probe to U15 pin 11. Type "30". Now when you type "60" you should observe a 40 millisecond positive going pulse. Move the probe to pin 8 of U15 and the pulse should be negative going. Now type "32" and repeat the above checks, the pulse should now be 1 millisecond. With a logic probe you will probably only be able to detect the presence of the pulse and will have to assume it is the correct length, with a test meter you probably won't be able to see anything!

Now switch off and insert U19. Connect a test meter set to about 500mA DC in line with the power input and switch back on. If the current is more than 100mA greater than it was before switch off and find out why! The most likely cause is a short circuit on VPP somewhere. If all is well remove the meter and connect the power directly. Set all four presets to the centre position.

Set a test meter to the 10V DC range and connect between pins 28 (+ve) and 14 (-ve) of the EPROM socket. Type "23" then "38", the meter should read 5V +/-0.25V. Now type "30" and the reading should rise, adjust RV1 for a reading of 6.1V +/-0.1V. Type "80" and the voltage should drop to zero. Set the meter to the 30V DC range and transfer the +ve meter probe to pin 1 of the EPROM socket. Type "34" and then adjust RV2 for a reading of 12.6V +/-0.1V. Type "30" and adjust RV3 for 21V +/-0.25V. Type "2F" and adjust RV4 for 25V +/-0.25V. Type "31" and the voltage should drop to zero.

The only thing left to check now is the various configurations for the different types of EPROM's. As described in "How it Works", the functions of six of the EPROM socket pins vary depending upon the type of EPROM. The address lines have already been checked at the EPROM socket, as has the programming voltage to pin 1. The checking of the remaining combinations is detailed below.

Line 100 opens the serial communications as before. Lines 120 to 300 attempt to establish communications with the programmer and test whether or not the CTS connection is present and working. Line 120 sets the program pulse duration to 40 milliseconds, initiates a program pulse immediately followed by a send instruction. If CTS is present the send instruction will not be sent until the program pulse has finished so data will be received, otherwise no data will be sent (see "How it Works - Hardware"). The integer variable PAUSE% is set to 1 if there is no CTS line, causing the software to add suitable delays itself - note that this will slow the operation of the software quite drastically.

Lines 150 to 280 send values to the data latches and then attempt to read them back - this is to establish that communication is reliable.

Lines 310 to 780 request information from the user regarding the EPROM type and programming requirements, whilst lines 790 to 820 set up the programmer accordingly.

Lines 1000 to 1230 form the main menu. Note that CHR$(27) gives the value of the Escape key.

The Read, Program and Verify sections use ASCII-HEX data files in the programmers own format (conversion programs to and from Intel-HEX are given later). The format is easy to produce and edit manually.

The first line is the name of the EPROM type - "2716", "2732" etc. The remaining lines each start with the address in Hex (4 digits), followed by four spaces, followed by 16 bytes in Hex (2 digits) each separated by one space. The addresses must be sequential, starting at 0000 (Table on a small section).

It should also be noted that this format is not particularly efficient with disk space - the file for a 27512 will take up about 250K. A file compression utility, such as PKZIP or LHARC, will dramatically reduce the size for storage if disk space is a problem.

With the information that has gone before, the operation of the remaining sections of the software should be fairly apparent.

The section from 2000 to 2300 reads the contents of the EPROM to a file. Lines 2100 and 2110 give a quarter second delay to allow the power supply rails to come up.

The section from 3000 to 3390 programs the EPROM from the contents of a file. Lines 3270 to 3290 add a delay (100 milliseconds) to allow for the programming pulse if the CTS line is not present, this will occur whether the programming pulse is 1 or 40 milliseconds. This delay may be optimised but it would be better to get CTS working in the first place.

The section from 4000 to 4330 verifies (or compares) the contents of the EPROM with a file, whilst the section from 5000 to 5240 checks the device is blank (all locations contain "FF"). The section from 6000 to 6220 allow the programming voltages to be checked.

The programs given in Listing 4 and Listing 5 convert the EPROM programmer data files to and from standard Intel-HEX data files respectively. This is not the place for an explanation of the Intel-HEX file format, so please just accept that the programs work! Details of Intel-HEX and other standard file formats are on the disk available from the author, together with various conversion programs etc.

In Use
The control software is shown in Listing 3 and is suitable for an IBM PC or compatible machine running BASICA, G.W.BASIC or QBASIC. This software is about the minimum required to make sensible use of the programmer. section.

If BASICA or G.W.BASIC is being used, the program will run fairly slowly. This is a limitation of interpreted BASIC. QBASIC supplied with MS-DOS 5 is a much more advanced product and a good deal better in this respect.

Additional (faster) software is supplied on the disk available from the author (downloadable from this website).

An EPROM must not be inserted or removed if the "Program" or "Read" LED is lit, or if the programmer is configured for a different type of device. 24 pin EPROM's must be fitted in the lower pins (3-26) of the socket. In all cases pin 1 is upwards. Failure to observe the above may result in damage to the EPROM or (less likely) the programmer.

The programmer should be switched on and connected to COM1 (RS232 serial port 1) on the computer. Start the software and the "Program" LED will light. Once successful communication has been established the program will request information about the type of EPROM and the programming method required. See the table below or consult the manufacturers data book.

Some 2764 and 27128 types require a complex arrangement of programming pulses however a single 1mS pulse will usually suffice. If in doubt or if problems are experienced use 40mS. Although some 2716 and 2732 devices will program successfully with a 1mS programming pulse, this is not recommended for final EPROM's, but may prove useful when testing software etc.

The use of the "A" suffix on 12.5V 2764 and 27128 types appears to be less than standard, it is suggested that all 2764's and 27128's should be tried on 12.5V first, since 21V will destroy a 12.5V device.

Once these selections have been made the "Program" LED will extinguish and the main menu will appear.

"Read" (menu option 1) reads the contents of an EPROM to a file. Note that the file format used is non-standard, however programs to convert to and from the Intel-HEX standard are given in Listings 4 and 5. The advantage of the file format is that it is easy to generate and edit manually.

"Program" (option 2) programs the EPROM from a file. The EPROM is not blank checked before programming or verified afterwards, these operations should be done from the main menu individually if required.

"Verify" (option 3) compares the contents of the EPROM with a file, and "Blank Check" (option 4) does as it's name suggests! Both these options report the number of locations that failed.

"Change Configuration" (option 5) re-starts the software so the EPROM type and programming method can be changed.

"Adjust Voltages" (option 6) allows the programming voltages to be checked and adjusted if required.

Happy programming!