How to determine the accurate model of MCU - Page 1
Forum section: electronics / repair

author: daisizhou
author_rank: Super Contributor
timestamp: April 21, 2023, 09:18:46 pm
content: Hallo every one.I am repairing a motherboard,Unfortunately, the three main MCU models on the motherboard have been removed,Through the remaining traces, I vaguely see the INTEL logoU13, I saw the XX53 Intel 80 logoAdditionally, I measured the VCC and GND pin definitions of three MCUs(The other definitions of pins are incorrect, I borrowed the definition from the 8088 package)I would greatly appreciate it if you could tell me the exact model number. Thank you

author: wasedadoc
author_rank: Super Contributor
timestamp: April 21, 2023, 09:30:43 pm
content: 8086 ?

author: daisizhou
author_rank: Super Contributor
timestamp: April 21, 2023, 10:33:01 pm
content: According to the pin definition of 8086, it seems to be inaccurate

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 21, 2023, 10:43:24 pm
content: Not sure if this is the rightmanual for this. No detailed schematics but it might help you somehow.QuoteDid you measure these using diode check (beeper)? If so, they may not be 100% correct. Measure on ohms range and make sure each pin measures less than 1to VCC or GND.

author: fzabkar
author_rank: Super Contributor
timestamp: April 21, 2023, 10:55:07 pm
content: QuoteI'm guessing U13 could be a PIA, eg something like an 8255A (unless there is an additional controller on the keyboard PCB), or an 8042, etc.Intel databooks of that era:https://mirrorservice.org/sites/www.bitsavers.org/components/intel/_dataBooks/I would determine which pins connect to the LEDs. They will probably be driven from an 8-bit port, or perhaps two 4-bit ports.The keyboard's 4 rows and 4 columns would be similarly connected, I would think.

author: daisizhou
author_rank: Super Contributor
timestamp: April 21, 2023, 11:26:43 pm
content: I repeated the measurements and confirmed that the resistance from VCC and GND to MCU pins is less than 1 ohm

author: daisizhou
author_rank: Super Contributor
timestamp: April 21, 2023, 11:30:44 pm
content: Give me some time to disassemble the keyboard and test the definition of the chip U13 connected to the keyboard. The key layout is indeed 4 rows and 4 columns

author: daisizhou
author_rank: Super Contributor
timestamp: April 22, 2023, 06:09:10 am
content: I have drawn the schematic diagram of U13 pin, but it is not complete. There is also one ULN2013A chip that has not been drawn yet

author: fzabkar
author_rank: Super Contributor
timestamp: April 22, 2023, 06:08:01 pm
content: U13 could be an 8279 / 8279-5.https://mirrorservice.org/sites/www.bitsavers.org/components/intel/_dataBooks/1987_Intel_Microprocessor_and_Peripheral_Handbook_Volume_2.pdf(page 352)http://www.elektronikjk.pl/elementy_czynne/IC/8279.pdf"The Intel 8279 is a general purpose programmable keyboard and display I/O interface device designed for use with Intel microprocessors."Where does the crystal go? Does it connect to one of the MCUs, or does it go to a clock generator?What is the Signetics IC at U8? Could U10 be an I/O expander, something like an 8243?Where do the DIP switches go? I expect they would go to an 8-bit MCU port.Where do the EPROM data and address buses go?The manual states that there are two 8-bit ports (LED and Function) on the Module Bus at J12. I expect that each would be buffered by an octal buffer/latch/transceiver, and these would connect to 8-bit ports on a controller, or perhaps they would connect to the data bus of the master CPU.

author: daisizhou
author_rank: Super Contributor
timestamp: April 22, 2023, 11:23:32 pm
content: I drew all the leads of the U13 chip pins.Unfortunately, part of the U13 leads are connected to U12, U10, and U9 have also been erased from their marks，From a functional perspective, U13 is only used for keyboard control and LED display.8279 seems that the pin definition and GND definition of VCC are not consistent with the actual circuit.U8 model is 74LS154N。DIP switch, I am looking for a circuitIn order to see clearly, I took a clearer picture againhttps://i.postimg.cc/ydNGRrBV/P30423-071816.jpg

author: fzabkar
author_rank: Super Contributor
timestamp: April 23, 2023, 12:08:55 am
content: I would concentrate on U15, U16, U21 and U22 ... and the crystal.Edit:Could pin #1 of U13 be shorted to ground via a fault condition? The unused row inputs are pulled high.Edit 2:Could U12 be an 8155H or 8156H 2Kbit SRAM with I/O ports and timer?https://pdf.dzsc.com/815/8155H.pdfEdit 3:The PROG pin on the 8243 I/O expander is a clock input, so it would match an 8279 at U13.https://www.cpu-galaxy.at/cpu/ram%20rom%20eprom/other_intel_chips/other_intel-Dateien/8243_Datasheet.pdfUsing the 8279 as a reference, pin #9 of U9 would be IRQ or INTR. U9 would be the main CPU (master).

author: daisizhou
author_rank: Super Contributor
timestamp: April 23, 2023, 08:31:09 am
content: Insert pins 1, 2, 5, and 6 of U13 into the sketch I drewI updated some pins for U12, but the measurement was difficult.I am still updating the route, hoping to find clues

author: daisizhou
author_rank: Super Contributor
timestamp: April 23, 2023, 10:08:59 am
content: I have updated some of the circuits and found that the crystal is connected to U19, which seems to be a "switch" function.It's also the first time I've encountered such a crystal oscillator circuitI will continue to draw the crystal oscillation circuit, which may take some time

author: daisizhou
author_rank: Super Contributor
timestamp: April 23, 2023, 01:33:12 pm
content: https://i.postimg.cc/mDQGHfj0/P30423-212525.jpgI used a magnifying glass to observe the remaining traces of U10 and found?? 827? Or?? 62? numberI am sending pictures hoping to provide clues

author: fzabkar
author_rank: Super Contributor
timestamp: April 23, 2023, 06:03:20 pm
content: It looks like I was wrong about the 8243 (I forgot that the chip was upside down). That said, I can't find any Intel chip of that period which matches the numbers you have identified.As for the clock circuit, Google offers several different examples:https://www.google.com/search?q=crystal+clock+"74LS04"&tbm=ischDo pins 10 and 11 of U13 connect to U9 (pins 32 and 31, respectively), and does pin 10 of U13 connect to the EEPROM OE* pins?https://deramp.com/downloads/mfe_archive/050-Component%20Specifications/Hitachi/Hitachi%20IC%20Memory%20Data%20Book.pdf(page 319)If I were reverse engineering this circuit, I would start with the known components and work backwards. For example, we know the pinout of the EPROMs, so we would trace the EPROM pins back to the main CPU. We also know the pinout of the 74LS154 4:16 decoder, so we could trace the inputs back to the same CPU. The latter would probably be connected to the address bus. I expect that at least some of the outputs of the 74LS154 would the CEs for the EPROMs.BTW, I found this site:https://www.ebme.co.uk/forums/ubbthreads.php/ubb/printthread/Board/30/main/11064/type/thread

author: daisizhou
author_rank: Super Contributor
timestamp: April 23, 2023, 09:29:27 pm
content: I am referring to the three DIP40 pin chips produced by INTEL（U13、U12、U9）,However, this U10, also known as 8243, does not seem to be produced by IntelNext, I will focus on drawing the crystal oscillator circuit and the EEPROM input circuit,74LS154 to MCU partial circuit

author: fzabkar
author_rank: Super Contributor
timestamp: April 24, 2023, 02:58:31 am
content: FYI, I have discovered that all the EPROM dumps have a checksum byte at offset 0xFF0. This is computed by summing the EPROM contents in the range 0 - 0xFEF. I don't know how to validate the last 15 bytes, though.

author: daisizhou
author_rank: Super Contributor
timestamp: April 24, 2023, 05:57:24 am
content: The A0-A11 and O0-O7 of the six EEPROM chips are all short circuited together. I tried to draw the connections between U1 and U2, and the others are the same connections.Unfortunately, the U7 has also been polished out of its model chip.I have taken a video of normal use and hope it can be helpfulhttps://youtu.be/Blup_MmSBbY"EPROM dump has a checksum byte at offset 0xFF0"This may be a zero position.I am still working hard to find the crystal oscillator circuit

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 24, 2023, 11:00:54 pm
content: Quote from: daisizhou on April 24, 2023, 05:57:24 amHopefully you mean A0 on one EEPROM goes to A0 on all the other EEPROMs; A1 on one EEPROM goes to A1 on all the other EEPROMs; A2 on one EEPROM goes to A2 on all the other EEPROMs etc...So, now find out which of the 40 pin ICs are also connected to A8-A11 of the EEPROMs. That will most likely be the CPU...It is highly likely that A0-A7 and D0-D7 are multiplexed onto the same pins on the CPU via something like a 74LS374, so A0-A7 of the EEPROMs may not be connected directly to the CPU.

author: fzabkar
author_rank: Super Contributor
timestamp: April 24, 2023, 11:12:00 pm
content: Quote from: Kim Christensen on April 24, 2023, 11:00:54 pmThat appears to be the function of U7. I have tried to trace the address and data pins (on the underside of the PCB), but some disappear into thruholes.This is my guess at the pinout of U7.Code:1 20 VccA7 2 19 A6O7 3 18 O6O5 4 17 O4A5 5 16 A4A3 6 15 A2O3 7 14 O2O1 8 13 O0A1 9 12 A0GND 10 11

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 24, 2023, 11:51:11 pm
content: Quote from: fzabkar on April 24, 2023, 11:12:00 pmThat looks a lot like a 74LS374 or 74LS373...If so, pin 1 would be tied low, and pin 11 would be connected to the ALE (Address Latch Enable) pin of the CPU.

author: daisizhou
author_rank: Super Contributor
timestamp: April 24, 2023, 11:57:48 pm
content: yes.What I mean is that the A0 pin of U1 EEPROM is directly connected to the A0 pin of U2 EEPROM,Also directly connected to A0 of U3, U4, U5, and U6,The remaining A1-A7 connections are the same.In the end, they all connected to U7 (The model has been removed).The same goes for O0-O7,Finally, they are also connected to U7.U1-U6 EEPROM CE pins are independently connected to U8 (74LS154N).The OE/VPP pins of U1 EEPROM are connected to the 32 pins of U9Please refer to the file I drew for detailsthanks

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 12:02:12 am
content: https://i.postimg.cc/02Yj6MzL/P30424-210538.jpghttps://i.postimg.cc/1zt3YvvQ/P30424-210557.jpgI took clear pictures, hoping it would be helpfulYes, drawing is very difficult, many wiring runs through repeatedly, and some are even lost in the circuit boardthanks

author: Psi
author_rank: Super Contributor
timestamp: April 25, 2023, 12:05:19 am
content: I have not read the entire thread but if you put some isopropyl alcohol on the chip it may make it easer to read.Another option, if you can find a camera without any optical filter on it, take 3 photos one illumined by white light, one with UV light and one with IR light. Try a few angles of the light as well.But using all methods combined you can often figure out the text.Of course this depends if there is some information left there to see. if it's totally gone then this is probably not worth the time.

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 12:06:13 am
content: Quote from: Kim Christensen on April 24, 2023, 11:51:11 pmI wonder why the manufacturer chose to scrub the markings off this jelly-bean chip?

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 12:16:13 am
content: The progress is very difficult, I don't know which part to focus on next, I'm a bit lost...............Removing the model may be due to the manufacturer's desire to monopolize after-sales service, repair, calibration, etc.They don't want a third party to repair this motherboard.This is also my initial idea of choosing reverse drawing,I hope to help users who are currently using this host because the manufacturer has stopped after-sales service.This is a mainframe produced around 1988

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 12:18:30 am
content: Quote from: daisizhou on April 24, 2023, 11:57:48 pmPlease excuse my ignorance, but which  tool can I use to view your .schdoc files?

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 12:19:17 am
content: Quote from: daisizhou on April 24, 2023, 11:57:48 pmI can't view any of the *.schdoc files (Don't have Altium) and I don't see a reference to U7 in the JPG or PDF files that you've posted so far. Perhaps I missed something?EDIT: I triedtheir online viewer, but it gave me an error message:Code:Please ensure all supported design or manufacturing files are included in the upload. Note that library files are not currently supported

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 12:23:02 am
content: As you can see, the method you mentioned may be feasible for U13, but the front half of the model is deeply worn, and only XX53 is visible at the rear。For other chips, such as U12, U10, U9, U7，They are deeply removed,There are several that only see an 'i' - intel mark

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 12:31:05 am
content: Could the CPU be an 8085 / 8085A / 8085A-2? (pins 8, 9, 10 don't appear to match, though)https://www.inf.pucrs.br/~calazans/undergrad/orgcomp_EC/mat_microproc/intel-8085_datasheet.pdfhttp://elektronikjk.pl/elementy_czynne/IC/8085-3.pdf

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 12:32:40 am
content: Sorry, can't I send the '. schdoc' file I posted?I drew the drawings online using "lceda. cn". If you cannot open them using Altium, please let me know. Of course, lceda. cn is free for online editing

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 12:35:21 am
content: Sorry, I will resend the PDF again

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 12:58:20 am
content: U9 looks to be a 8085A CPU judging by U9-30 (ALE) going to U7-11Plus, the fact that A8-A11 of the EPROMs go to pins 21, 22, 23, & 24 of U9 point toward it being an 8085A.Now check if pins 13, 8, 14, 7, 17, 4, 18, & 3 of U7 go to pins 12-19 on U9... These are the multiplexed lower 8bits of the address buss and data buss.

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 01:04:58 am
content: Quote from: Kim Christensen on April 25, 2023, 12:58:20 amWhat do you think about pins 8, 9, 10?

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 01:22:51 am
content: Quote from: fzabkar on April 25, 2023, 01:04:58 amIf U9isa 8085A...They appear to be active high interrupt input pins. 8 & 10 are tied to ground so are not used. Pin 9 is also an interrupt pin and looks like it receives interrupts from the keyboard chip U13..

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 02:19:32 am
content: I measured the corresponding relationship between U7 and U9 as shown in the table below, which is exactly the same as what you analyzed(U7-13 -> U9-12U7-8 -> U9-13U7-14 -> U9-14U7-7 -> U9-15U7-17 -> U9-16U7-4 -> U9-17U7-18 -> U9-18U7-3 -> U9-19)Do I need to test more pins? Please let me know if neededthanks

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 02:38:04 am
content: Can I use a digital oscilloscope to test the unknown pins of U9?What I mean is to use a digital oscilloscope for testing and ultimately confirm whether it is the 8085A model or another modelIf you need me to test more pins, please let me knowthanks

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 02:52:02 am
content: If you measure the frequencies of the clock pins on the MCUs, that will tell you if you need the higher speed versions.Try to determine where pins 36 and 37 connect (RESET IN and CLOCK OUT).Pin 8 of U12 (CE or CE*) would probably be driven by one of the outputs of the 74LS154. This will tell us whether U12 is an 8155 or 8156.

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 03:04:50 am
content: Is it meaningful for me to operate this way?I want to know if U9 is 8085AU9-P36 connected to J6-P20.U9-P37 connected to J5-P13 、U10-P18、 U13-P3U12-P8 connected to J8-P1、U8（74LS154N）-P5

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 04:15:42 am
content: U12 could be an 8155 but not an 8156 because the outputs of the 74LS154 are active low.U9-P37 is a CLOCK OUT. This is consistent with a CLK input at U13, so U13 could be an 8279.If U9-36 is a RESET input, then it must be generated onboard. Since it is active low, it could be implemented with a simple RC circuit. Often there will be a small, ground connected tantalum capacitor and a series resistor (C15 and R6 near J6 ?). The RESET pin would connect to the junction of the capacitor and resistor.I don't know how to distinguish between and 8085 and an 8085A. FWIW, Google says ..."8085A is bug fixed version of 8085 and almost immediately replaced it. There are also differences in clock designated by latter H, eg 8085A is 3MHz, 8085AH is 5MHz. Manufacturers usually add letter to designate minor changes, like bug fixes or improved fab process, etc."U7 is probably a 74LS373 rather than a 74LS374.See page 60 for a circuit example:http://www.frankshospitalworkshop.com/electronics/documents/Electronics%20For%20You%20-%20Projects%20and%20Ideas%202000.pdf

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 04:50:29 am
content: Quote from: fzabkar on April 25, 2023, 04:15:42 amYes, I think U13 is an 8279... U13-4 (interrupt out) is connected to one of the interrupt inputs on U9-9 (8085A)...Plus, the circuitry around the 8279 is very similar to the example circuit attached.QuoteThere was a bug in the original 8085... The 8085A is identical minus the bug.QuoteI'm leaning that way to... U12-2 being grounded is a bit odd/confusing, but not totally out of line if it was an 8155.And U10 might be an 8253 timer. I'm making some notes on the diagram... Just not done yet.

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 05:05:11 am
content: I think you're right about the timer:https://www.cpcwiki.eu/imgs/e/e3/8253.pdfThe order of the OUT pins matches an 8155, and the two clocks go to the right places (PA 5/6/7 -> OUT 0/1/2).Code:D0 1 24 VccD1 2 23D2 3 22D3 4 21 U20-8D4 5 20D5 6 19 A0 (U13)D6 7 18 CLK OUT (U9)D7 8 17 PA7Clk 9 16 PB1PA5 10 15 PC0PC1 11 14 PB4GND 12 13 PA6I found that the 8254 is an improved, high speed version of the 8253:https://www.scs.stanford.edu/10wi-cs140/pintos/specs/8254.pdfhttps://kader05cuet.files.wordpress.com/2014/09/8254.pdf(diff between 8253 and 8254)As for the part marking, I think we are seeing the second line. The part number is on the first line.https://i.ebayimg.com/images/g/0n4AAOSw3ZBiAeQO/s-l1600.jpg

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 05:37:32 am
content: Another thing to confirm chip type, would be to trace the WR and RD pins from the CPU (8085) to these peripheral chips to see if they match the pinouts.I've noticed that the RESET out from the 8085 also lines up properly with our "estimated" chips that have a RESET input.EDIT: Another thing to check would be to see if IO/M on the U12 (pin 7) connects to IO/M on U9 (pin 34).

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 05:40:07 am
content: Your analysis is very accurate, U9-P36 is connected to J6-P20 and then to C15 and R6Do I directly update the confirmed chip model and pin definitions on the schematic diagram I have drawn? Does this help with reading?

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 06:09:40 am
content: Yes, that's helpful.

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 07:55:54 am
content: I have updated the definition of pins, hoping it will be helpful for reading and analysis,Do you still need to measure unknown test point connections? If necessary, please let me know the specific testing locationthanks

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 10:40:18 am
content: U3 and U2 must be the boot ROMS. The labels on the PCB correspond to the base addresses of each ROM.

author: daisizhou
author_rank: Super Contributor
timestamp: April 25, 2023, 11:34:17 am
content: Do you mean that the system firmware exists internally in U2 and U3?U1, U4, U5, and U6 store calibration data?Do you know what purposes EXPANSION NO1 (J6), EXPANSION NO2 (J5), INTERFACE (J4), AUX. INTERFACE (J3), and J2 are used for?I found an RS-232 interface vacancy and a GPIB-488 interface vacancy at the back of the host.Can I re-establish them on the motherboard?Have you found any RS232 and GPIB-488 traces in the firmware? I guess these interfaces may be used for calibration or computer online software communication

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 05:58:25 pm
content: Quote from: daisizhou on April 25, 2023, 11:34:17 amI have done this with similar equipment, but it also needed a firmware upgrade. Luckily for me, I had an identical unit with the GPIB option installed, so I just copied it's EPROMs to make the other one work.To examine the code, you could figure out what IO or memory address the missing RS232/GPIB chips use. (By looking at what their CE [Chip Enable] pins would connect to) U8 appears to be involved in memory mapping for the EPROMs and U12-8. (The entire IO might be memory mapped) But U20 seems to be involved as well (It feeds U13-22 & U10-21), but not all it's pins are traced out. Figuring out where U9-34 (IO/M) goes can help determine whether U13 & U10 are memory or IO mapped, and thus give us a clue how your missing chips might be mapped as well.Once you know the IO or memory address, that the missing RS232/GPIB chip's will use, you could search the code to see if it accesses any of those addresses.

author: fzabkar
author_rank: Super Contributor
timestamp: April 25, 2023, 06:15:52 pm
content: I found this simple 8085 disassembler:https://sites.pitt.edu/~rick/db8085.zipThere are probably better tools, but it's a start. I concatenated U3 and U2 into bootroms.bin, and I then disassembled the combined file.I found these I/O instructions:Code:OUT 40H 42H 44H 45HIN 40H 41H 43H 44H 45HU4 and U5 contain calibration data.U1 and U6 contain code.

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 25, 2023, 11:41:51 pm
content: Quote from: fzabkar on April 25, 2023, 06:15:52 pmLooks like the 8155 is the only chip that's accessed via IO mapping in that code... All the other chips are probably memory mapped. Took me a while to decipher, until I realized that the 8085 puts the same duplicate IO address byte on both the lower and upper 8bits of the address lines. Kind of makes sense since the 8155 contains both RAM and IO in the same address space. U9-34 must be connected to U12-7 for this to work (IO/M).So for example the 4 in 42H is decoded by U8 which drives U8-5 low and thus the 8155's chip select U12-8. The 2 selects the General Purpose IO port-B via the lower address lines.Therefore all those OUT and IN codes (40H to 45H) are commanding and reading from the 8155.

author: daisizhou
author_rank: Super Contributor
timestamp: April 26, 2023, 01:17:15 am
content: thanksI updated U8, U9, U12, U9... circuit.There may be some missing circuits,If you find out, please let me know and I will complete the circuit(Can the. png and. pdf files be clearly viewed? If not, please let me know)

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 01:52:02 am
content: Yes, the PNG and PDF files look good to me (I had to install the Asian font pack for Acrobat Reader).Can you find out if U13-21 (A0) and U10-19 (A0) and U10-20 (A1) connect to the 8085? These signals need a source.I can see lots of RIM and SIM opcodes in the disassembled source. These are new to the 8085A, so I'm reasonably certain that the CPU is an 8085A rather than an 8085.

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 26, 2023, 03:06:48 am
content: Quote from: fzabkar on April 26, 2023, 01:52:02 amI would guess that those would be connected in parallel with their corresponding EPROM address lines and not directly to the 8085:U13-21 (A0) and U10-19 (A0) should connect to U3-8 for example.U10-20 (A1) should connect to U3-7.The demuxed A0 - A7 are all driven by U7.I think I figured out the memory mapping of the Keyboard controller U13 and the Timer IC U10U10 (8253) base address is 5000H (Timer)U13 (8279) base address is 5800H (Keyboard controller)This is assuming I didn't get my wires crossed.

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 04:12:52 am
content: Quote from: Kim Christensen on April 26, 2023, 03:06:48 amYou beat me to it. I was just about to amend my post.

author: daisizhou
author_rank: Super Contributor
timestamp: April 26, 2023, 04:26:15 am
content: U13-21 (A0) and U10-19 (A0) connected to U9-P21U10-20 (A1) connected to J5-P15, U9-P22Are there any other pins?If you have any questions, please let me know as much as possible and I will measure them

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 04:52:14 am
content: Quote from: daisizhou on April 26, 2023, 04:26:15 amThose are A8 and A9.That would make the base addresses for the 8279 and 8253 to be 0x5100 and 0x5300, would it not?

author: daisizhou
author_rank: Super Contributor
timestamp: April 26, 2023, 05:04:54 am
content: YES.Is there anything else I need to do?

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 05:17:50 am
content: What do you want to do? I think the ICs have been identified. Wasn't that your aim?

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 26, 2023, 05:32:51 am
content: Quote from: fzabkar on April 26, 2023, 04:52:14 amNo, I don't think that changes the base addresses. We still have an inverted A11 (Via U19) from the 8085 OR'd (via U20) with the 5000H from U11-6.What it changes is how they are indexed... Initially I thought it would go like this for U13:5800H vs 5801H for command or status register.But instead it's5800H vs 5900H for command or status register.And now U10 would be:5000H, 5100H, 5200H, 5300H, etc for each successive register.** Or my brain could be borked because it's late here. Heading to bed now...

author: daisizhou
author_rank: Super Contributor
timestamp: April 26, 2023, 06:10:00 am
content: Thank you again for confirming the chip model.Do you know the purpose of these interfaces? {EXPANSION NO1（J6），EXPANSION NO2（J5），INTERFACE（J4），AUX.INTERFACE(J3)，J2},They look like extension interfaces。I found an RS-232 interface vacancy and a GPIB-488 interface vacancy behind the host. Can I recreate them on the motherboard? Have you found any traces of RS232 and GPIB-488 in the firmware? I guess these interfaces may be used for calibration or computer online software communication.My idea is, is it possible to create an interface board in my spare time to achieve RS232 or GPIB-488 communication functions.Enable communication between motherboard and computer to achieve test data storage or regular calibration of host operations.For example, adding a LCD screen to convert data into waveform output display

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 06:18:20 am
content: Quote from: Kim Christensen on April 26, 2023, 05:32:51 amYes, of course you're right. I've had a medical issue today, so I'm not thinking straight. <slaps forehead>

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 26, 2023, 04:04:09 pm
content: Quote from: daisizhou on April 26, 2023, 06:10:00 amPost a picture of this PCB/area. If it is a PCB, and not just some labeled holes in the chassis, then you could see if there are any connections between U9 (8085) and one of the larger empty IC footprints. Try tracing these pins from U9:3 (reset out)31 (WR)32 (RD)12-19 (data buss)QuoteI'm no expert on 8085 coding, but knowing the IO addresses of those RS232/GPIB chips can help us search the code more easily. So I think we need to figure out the missing hardware first.QuoteIf we can't figure out the "RS-232 and GPIB-488 interface vacancy" (Or your firmware doesn't support it) one hack could be to use a micro to decode the display data sent to U13 (8279), convert it to RS232, and send it to a PC. The same micro could be used to receive RS232 commands from the PC, and then stimulate U13's keyboard interface. (It would be a slow method of commanding the RT-200, but it would work)

author: fzabkar
author_rank: Super Contributor
timestamp: April 26, 2023, 11:44:03 pm
content: I'm curious about pin 23 of the Module Interconnect Bus (pages 36 and 41 of the manual). I wonder where it goes? 8253?QuoteQuote

author: daisizhou
author_rank: Super Contributor
timestamp: April 27, 2023, 12:18:15 am
content: I checked the PCB motherboard and found that these four hole positions look like installation column screw hole positionsI guess the PCB may be installed on the screw column，May be connected to J3, J4, and J2 through flexible cablesI searched for U9's (RESET, WR, RD, data buses) and found that they were connected to the J5 interfaceIn addition, I have updated the circuit of the J2 interface section, hoping it will be helpful for analysis

author: daisizhou
author_rank: Super Contributor
timestamp: April 27, 2023, 12:44:20 am
content: J12-P23, ultimately connected to U19-P9

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 27, 2023, 02:49:59 am
content: From page 4-1 of manual:QuoteNowhere in the manual do I see anything about GPIB or Serial options. Most manuals would list the command set for those interfaces if they existed.

author: daisizhou
author_rank: Super Contributor
timestamp: April 27, 2023, 04:14:32 am
content: As you said, I track the RD WR signals and they are connected to U14,I also updated U15, U16, U17 with ease,Not all U15 and U16 have been completed yet

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 27, 2023, 05:08:02 am
content: Looks like U15 (out) & U16 (in) might be set up as an 8bit IO port connected to the J3/J4 interface. They are mapped to the 6000H address. There are some references to this address in the code as well...

author: daisizhou
author_rank: Super Contributor
timestamp: April 27, 2023, 08:43:05 am
content: I have further completed the schematic diagram,If there is anything else you don't understand, please let me know.thanks

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 27, 2023, 04:47:42 pm
content: A couple of things that don't look right so far:

author: daisizhou
author_rank: Super Contributor
timestamp: April 28, 2023, 01:26:47 am
content: U10-P8 is an incorrect connection.U17-4 and U17-3 are connected to programming switches S1-S8, and the setting of the board is that S1-S6 is connected to the negative electrode, while S7 and S8 are in open circuit.I have drawn the circuit for S1-S8, and now I understand some unreasonable pin grounding for U9 and U12EEPROM chips U1 and U2 have a jumper to control their reading or writing - J1

author: fzabkar
author_rank: Super Contributor
timestamp: April 28, 2023, 04:50:57 am
content: J1 connects pin #21 of U1 to either A11 or WR*. In other words, J1 selects whether U1 is treated as an EPROM (A11) or a static RAM (WR*).A 6116 SRAM fits the pinout:http://www.princeton.edu/~mae412/HANDOUTS/Datasheets/6116.pdfI guess a 2816A EAROM could also fit the pinout:https://deramp.com/downloads/mfe_archive/050-Component%20Specifications/Intel/Memory%20Components/Intel%202816A.pdf

author: daisizhou
author_rank: Super Contributor
timestamp: April 28, 2023, 08:18:38 am
content: I guess when writing the program, it was done on the J2 interface，Because the - WR signal of the J2 interface is connected to the J1 jumper,The J1 interface is now P2-P3 connected, and P1-P2 is connected when the program needs to be written.But strangely enough, it seems that the J2 interface is not a standard interface