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| Re: Starting V20 CPU on breadboard. [message #6943 is a reply to message #6940] |
Mon, 20 January 2020 11:16   |
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just4fun
Messages: 273
Registered: May 2017
Location: Dark side of the Moon
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Senior Member |
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gbm wrote on Mon, 20 January 2020 12:55Please look up my topic on SDC_One...
Hi gmb,
I've seen your topic and it is very interesting.
What I'd like to do is a little board that runs at "normal" speed (i.e 4/8MHz) with 1MByte RAM (all the address space) where the "companion" MCU do all the I/O stuff.
The breadboard is only for the first phase to check the boot sequence and the I/O "handshaking" between the V20 and the MCU (and others details), so using a breadboard (that is almost wired now) is needed to do "experiments".
In the final design I've the intention to use an Atmega32 as MCU (because I want use only THP parts in the final board), so the STM32 is only for the first step.
Anyway thanks you for your kind offer.
Fabio
[Updated on: Mon, 20 January 2020 11:22] Report message to a moderator |
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| Re: Starting V20 CPU on breadboard. [message #7116 is a reply to message #7033] |
Wed, 19 February 2020 12:11 |
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just4fun
Messages: 273
Registered: May 2017
Location: Dark side of the Moon
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Senior Member |
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I've done some HW changes and added an "I/O" led:
Now it is possible boot directly from a binary file on a microSD end execute it with the V20 CPU running at 8MHz.
Here the classic "Hello world" test:
I'm using now the NASM assembler:
;
; Test HelloWord - HW ref: A090120 (V20 on breadboard)
;
; REQUIRED: IOS S010220 DEVEL_16 (STM32F030R8)
;
; Assemble with "nasm -f bin filename.asm -o filename.bin"
;
[map mapFile.txt] ; Set output map file
CPU 8086 ; Set 8086/8088 opcodes only
BITS 16 ; Set default 16 bit
eos equ 0x00 ; End of string
; IOS equates
EXC_WR_OPCD equ 0x00 ; Address of the EXECUTE WRITE OPCODE write port
EXC_RD_OPCD equ 0x00 ; Address of the EXECUTE READ OPCODE read port
STO_OPCD equ 0x01 ; Address of the STORE OPCODE write port
SERIAL_RX equ 0x01 ; Address of the SERIAL RX read port
SYSFLAGS equ 0x02 ; Address of the SYSFLAGS read port
SERTX_OPC equ 0x01 ; SERIAL TX opcode
org 0
;
; Init
;
mov ax, cs ; DS = SS = CS
mov ds, ax
mov ss, ax
mov sp, stack ; Set the stack
;
; Print a message and halt
;
mov bx, msg
call puts
halt:
hlt
jmp halt
; =========================================================================== ;
;
; Send a string to the serial line, BX contains the pointer to the string.
; NOTE: Only AL and BX are used
;
; =========================================================================== ;
puts:
mov al, [bx] ; AL = current char to print
cmp al, eos ; End of string reached?
jz puts_end ; Yes, jump
mov al, SERTX_OPC ; AL = SERIAL TX opcode
out STO_OPCD, al ; Write the opcode
mov al, [bx] ; AL = current char to print
out EXC_WR_OPCD, al ; Print AL
inc bx ; Increment character pointer
jmp puts ; Transmit next character
puts_end:
ret
msg db 'Hello, World!', 0x0d, 0x0a, eos ; 0x00 is the message terminator
times 0x100 db 0;
stack:
Now more tests but it's probably time to start thinking at the final PCB version... 
[Updated on: Wed, 19 February 2020 12:26] Report message to a moderator |
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| Re: Starting V20 CPU on breadboard. [message #7301 is a reply to message #7298] |
Fri, 20 March 2020 18:33 |
rvumbaca
Messages: 17
Registered: September 2018
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Junior Member |
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Hi just4fun,
Just a warning that the chip markings on your V20 CPUs in your first post are consistent with re-marked chips.
That is, they are probably not really 16MHz parts, but re-marked parts that were originally rated at a lower speed (such as 8Mhz or 10Mhz). I can tell you more about this if you are interested.
This is a common issue with many retro and legacy parts. If you bought these parts from EBay and they came from Asia (for example China), then there is a high likelihood of this situation.
Therefore I just wanted to warn you that if you ever clock your chips at a high speed and you run into unusual behaviour, you do not have to blame your design!
Best regards and good luck with your project!
[Updated on: Fri, 20 March 2020 18:34] Report message to a moderator |
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| Re: Starting V20 CPU on breadboard. [message #7317 is a reply to message #7310] |
Sun, 22 March 2020 03:24 |
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just4fun
Messages: 273
Registered: May 2017
Location: Dark side of the Moon
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Senior Member |
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@rvumbaca:
Thanks very much for the warning! Yes, I've bought the CPU on ebay (as usual)...
The final board will use a 4/8 MHz clock, so accordingly with the V20HL datasheet the lowest speed grade is 10MHz and it is fine.
Up to now I've used no more than 8MHz as clock, anyway the breadboard prototype can set higher clock using a STM32F030 running at 48MHz, so I'll do some test just to see.
If you can give more info about the labeling I'm curious to know...
@cmacarthur:
I haven't tested the board yet, so I can't say if it works or not. However if you want try to produce it "at your own risk" I've attached the gerber for JLCPCB and the corresponding schematic.
[Updated on: Sun, 22 March 2020 03:32] Report message to a moderator |
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| Re: Starting V20 CPU on breadboard. [message #7321 is a reply to message #7317] |
Sun, 22 March 2020 15:22 |
rvumbaca
Messages: 17
Registered: September 2018
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Junior Member |
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Hi just4fun,
just4fun wrote on Sun, 22 March 2020 03:24@rvumbaca:
If you can give more info about the labeling I'm curious to know...
Long back story: In recent years there has probably been some renewed demand for legacy ICs such as CPUs and EPROMs, which are no longer manufactured. The IC counterfeiters of the world took the opportunity to profit from this. I can only assume that people often search for higher speed rated parts, as this seems to be a common reason for many re-marked Motorola, Zilog, Intel and other CPUs. Another common item is that slower speed EPROMs are re-marked as higher speed parts (and also the brand is changed). So if you search for "ST 27C400", you will find many, many re-marked parts (my programmer can read the ID code, often I have found that these are re-marked Macronix or National parts).
Most of the supply of these parts comes from a few warehouses in Asia. 99.9% of the sellers on EBay do not hold stock, they simply act as a seller and when you order a part they either buy it from these warehouses (or a distributor) or (more commonly) they arrange for drop-shipping from the warehouse/distributor direct to you. Often I found that ICs I bought from China or HK, are posted to me directly from the Philippines, Brunei, and other countries in Asia. When I have complained about the parts being counterfeit, the seller will often perform an immediate refund with no questions asked. The sellers have little knowledge of what they are selling, they often offer thousands of different items (sometimes not just ICs). Sometimes the picture looks good, but the part you receive is not the marked the same way.
The re-marking of chips exists at different "quality levels". The simplest method, is to paint over and use ink. If you rub these ICs with IPA or Acetone the ink often can be removed.
-> Try to rub the top of your IC with acetone or IPA and check if the marking is removed.
"Higher quality" re-marked chips usually have been ground on top, then a "black top" is applied. They then use laser engravers to re-mark the chip. Usually the markings have mistakes in them such as:
- Colour of marking does not match a part from that time
- Invalid date codes (for example a MC68010 with date code of 2019!)
- Many, many parts have the same batch code
- The marking does not match the original part
To see a great example of what "black top" and laser engraving looks like on an MC68000, see this photo from a colleague: https://twitter.com/SushiL0gic/status/1116219450708021248/ph oto/1
Recently I made a special effort to buy a real NEC V20. I was tired of receiving counterfeit parts, so I bought it from a seller in the USA. This is the appearance of my part:
Here is an image of your NEC V20 with signs of re-marking highlighted:
The counterfeiters have improved their process, but they still lack attention to detail :)
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Attachment: Re-marked.png
(Size: 88.47KB, Downloaded 1829 times)
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Attachment: NEC-V20.png
(Size: 860.31KB, Downloaded 1855 times)
[Updated on: Tue, 24 March 2020 15:30] Report message to a moderator |
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