VT101 8085 CPU Fault

Robert Jarratt robert.jarratt at ntlworld.com
Mon Jan 19 23:06:02 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Matt
> Sent: 19 January 2015 23:23
> To: cctalk at classiccmp.org
> Subject: Re: VT101 8085 CPU Fault
> On 19/01/2015 21:45, Diane Bruce wrote:
> > I'd suspect RAM since the ROM is (I assume) masked ROM.
> The masked ROM could be faulty. My VT100 character generator ROM failed
> with one of the data lines floating because (I think) one of the internal
> had became detached from the die. I replaced it with an EPROM but had to
> a few jumper wires to the legs of the chip to get the select lines in the
> combination.

I like the idea of swapping the ROM for an EPROM (whether to write my own
test code, or just to replace with a fresh ROM image - assuming I can find
one). I'll probe the ROM pins at the weekend to see if it appears to be OK.

Do you recall what EPROM you used and how its pinout differed from the ROM
you were replacing? As far as I can tell there is only one ROM on the board,
could it be both the character ROM and the firmware?



More information about the cctalk mailing list