22 Feb
2003
22 Feb
'03
4:56 p.m.
Thanks Eric,
I'll take your word for it since I haven't looked at an Apple 1
schematic for about twenty-five years! That may have been another reason
I didn't put video on my board!
Bryan
Eric Smith wrote:
Your Apple 1 homebrew page is interesting, but the
details about
Woz's design aren't quite correct. The Apple 1 did use 4K multiplexed
address DRAMs (typ. MK4096) for the main memory. But the video memory
was entirely separate, and consisted of seven Signetics 2504 1Kbit
dynamic shift registers and a Signetics 2519 hex 40-bit shift register.
The video memory recirculated constantly, so it didn't need any explicit
refresh circuitry.
It wasn't until the Apple 2 design that Woz shared the main memory with
the display to get automatic DRAM refresh.
Best regards,
Eric Smith