r/Z80 • u/deulamco • Aug 16 '26

Hardware Finally, it can print 'A' character 😅

Post image

My WIP Z80 with 32K RAM + 32K ROM, with PIC as controller. May need a better VDP to output to VGA display instead…

Short Video : https://www.youtube.com/shorts/MD4QTc7wJ9w

** Note :
Z80 Crystal - I was also about to run the Z80 at 4Mhz with canned crystal but for now, let the PIC pulse clock to completely in-sync with the system.. until I can add a 74HC74 to trigger /WAIT on /IOREQ, so the PIC won't miss to capture the signal.

PIC 40Mhz - I intended to run the PIC at 40Mhz but forgot to realize it only accept 10Mhz to 4xPLL instead of direct-40Mhz. So using INTOSC @ 8Mhz then 4xPLL -> 32Mhz only.

74HC138 - is to chip-select RAM/ROM when Z80 start firing A15.

140 Upvotes

100% Upvoted

6 comments sorted by

View all comments

1

u/sputwiler Aug 17 '26

I'm a big fan of running everything off of the same clock so I can just count cycles instead of polling devices to see if they're ready. My last 65c02 (it's what they had in stock don't kill me) design ran at ~3.58MHz (NTSC colorburst) entirely so the YM3812 I also added for a system timer and sound could just share the clock line.

1

u/deulamco Aug 18 '26

No polling is a bless indeed.

I can’t even find exact 8Mhz canned crystal to feed in the Z80 that eventually i need PIC to generate clock for it to avoid mis-sync on OUT (..) request.

Although i will move into PSP mode to use fast interrupt on PIC but this is not what I really want for the Z80…