Sinclair ZX80 / ZX81 / Z88 Forums

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.

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

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.

Thanks both. In that case I may as well bundle it with my other centronics items.

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…]

Hello,

I'm interested by your card, could you contact my PM to discuss about it?

Thanks
Yann

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.

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