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RS232 Interface (8255 Chip) £30
Posted: Tue Sep 22, 2020 8:02 pm
by Erm
On offer here for £30 plus whatever postage costs, is a ZX81 RS232 interface. Manufacturer unknown (it's most probably a German made product - Weidner is on the PCB). It uses a National Semiconductor INS8255N chip to do the business. I cannot test it, but if it doesn't work I'll gladly take it back.
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 23, 2020 3:33 pm
by 1024MAK
Hi Chris
I think that interface is actually a parallel ‘user’ port rather than a RS232 interface.
The main chip (INS8255N), is a PIA (see the attached datasheet), there are no voltage level shifters for the line to the 25 way D connector and there is no crystal for the baud rate clock generation.
Mark
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 23, 2020 6:00 pm
by XavSnap
Hi,
Yes, it's an (another!) Centronics card… too many datas on the socket, it's a female subd25 and there's no cristal/max232 components.
But, with a 8255, you can send a serial data on the socket… with a good zx81 program.
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 23, 2020 6:01 pm
by Erm
Thanks both. In that case I may as well bundle it with my other centronics items.
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 23, 2020 6:21 pm
by XavSnap
The both IORQ (data/command) had to be retrieve.
Asm driver from the 8255 simulator on Vb81:
[edit: ROM Driver from the Micro-Systèmes #47 :
http://zx81.ordi5.free.fr/brico/ui
https://www.abandonware-magazines.org/a ... =64&page=3
]
[edit2: the 24 I/O (PIA,PIB & PIC) are connected on the SUB 25 socket, can't be use on a Centronics printer, but the ground can be picked up on the card…]
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 30, 2020 8:44 am
by YannFr
Hello,
I'm interested by your card, could you contact my PM to discuss about it?
Thanks
Yann
Re: RS232 Interface (8255 Chip) £30
Posted: Wed Sep 30, 2020 8:37 pm
by Erm
YannFr wrote: ↑Wed Sep 30, 2020 8:44 am
Hello,
I'm interested by your card, could you contact my PM to discuss about it?
Thanks
Yann
Done that.
Re: RS232 Interface (8255 Chip) £30
Posted: Mon Oct 05, 2020 7:52 am
by XavSnap
To code a little driver, i built a Kicad project from the french "Micro-Systèmes" #47: "interface universelle" with a 8255 PIO.
Monitor ROM & PCB:
http://abandon.pcbs.free.fr/MicroSystemes.htm
http://abandon.pcbs.free.fr/MicroSystem ... le_n47.pdf