From 32f64dfce658fea5f3d8b9247055976b75020098 Mon Sep 17 00:00:00 2001 From: AJR Date: Fri, 22 Jan 2021 11:12:38 -0500 Subject: [PATCH] mac128.cpp: VIA note --- src/mame/drivers/mac128.cpp | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/src/mame/drivers/mac128.cpp b/src/mame/drivers/mac128.cpp index 96678472ace..5023a2cb587 100644 --- a/src/mame/drivers/mac128.cpp +++ b/src/mame/drivers/mac128.cpp @@ -52,7 +52,7 @@ Control B: 02 select WR2 00 int vector = 0 03 select WR3 -c0 8 data bits, Rx disabled +oc0 8 data bits, Rx disabled 0f select WR15, external interrupt status/control 08 enable 08 00 select WR0 @@ -80,6 +80,22 @@ c0 8 data bits, Rx disabled 09 select WR9 0a enable MIE / NV +VIA notes: + +Original 128K Macs use Synertek SYP6522 VIAs. Synertek's AN5 (March 1982) +claims that their VIAs have a difference in shift register behavior +compared to those from other manufacturers. However, this particular +difference is not relevant to the Mac hardware, and later 512K Macs +switched away from SYP6522 (Apple part number 338-6522-A) to either +Rockwell R6522AP (R6522-66) or VTI VL6522-02PC. R6522AP is the most +common VIA on the Mac Plus. + +Apple continued sourcing VIAs from the same two manufacturers for the +Mac SE, though their ADB-era VIAs are newer CMOS models with a fix for the +shift register's CB1 input synchronizer which Apple may have specifically +requested. The new Rockwell version (R65NC22) is only labeled with Apple +part number 338-6523 (later Macs use a PLCC version which Apple numbered +338S6523), but VLSI Technology's VL65C22V-02PC is not so disguised. ****************************************************************************/