6 Aug
2002
6 Aug
'02
6:50 p.m.
Ross Archer wrote:
r65c02p2 wrote:
>--- In 6502ag@y..., "rey_bbs" <rey_bbs@y...> wrote:
>
>
>>Is there a way to use 8255 in a 6502 computer instead of a 6522?
>>
>>
>Howdy Guys,
>
>I've read the list discussion regarding 8255's and the 6502 and
>thought I'd pipe up. I use 8255's with 6502 whenever I need lots
>of I/O bits per package count. Interface is rather simple. I also use
>NEC part Nr. D71055C which is a 8255 pin/program compatible CMOS
>component that will work to 10 MHz. Also using 82C55 for battery
>powered systems. All work quite reliably.
>
>The /RD and /WR signals for the 8255 I generate this way:
>
>/RD is 6502 R/W NAND Phi2
>/WR is 6502 INVERTED-R/W NAND Phi2
>
>Easily accomplished with single quad NAND...I generally use these
>same strobes for memory access and other buss connected device access.
>
> Regards All,
> Brian
>
Hi, and thanks for that. The cool thing is you've just generated
Z80-compatible strobes.
Don't forget to use that last NAND gate left in your 7400
to invert the reset signal from 6502 pin 40 into 8255 pin 35.
If not inverted, the 6502 RESET will hold the 8255 in reset
indefinitely, and if omitted, may not come up 100%. Correct?
-- Ross
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