From d4fb17a901af26c8851fdc0cbb66d54177176de7 Mon Sep 17 00:00:00 2001 From: AJR Date: Sun, 5 Mar 2017 13:44:08 -0500 Subject: ay8910: Handy guide to bus control signals (nw) --- src/devices/sound/ay8910.cpp | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/src/devices/sound/ay8910.cpp b/src/devices/sound/ay8910.cpp index e2e620ac4f1..0f92d483c46 100644 --- a/src/devices/sound/ay8910.cpp +++ b/src/devices/sound/ay8910.cpp @@ -227,6 +227,28 @@ Envelope shapes: The envelope counter on the AY-3-8910 has 16 steps. On the YM2149 it has twice the steps, happening twice as fast. +**************************************************************************** + + The bus control and chip selection signals of the AY PSGs and their + pin-compatible clones such as YM2149 are somewhat unconventional and + redundant, having been designed for compatibility with GI's CP1610 + series of microprocessors. Much of the redundancy can be finessed by + tying BC2 to Vcc; AY-3-8913 and AY8930 do this internally. + + /A9 A8 /CS BDIR BC2 BC1 + AY-3-8910 24 25 n/a 27 28 29 + AY-3-8912 n/a 17 n/a 18 19 20 + AY-3-8913 22 23 24 2 n/a 3 + ------------------------------------ + Inactive NACT 0 0 0 + Latch address ADAR 0 0 1 + Inactive IAB 0 1 0 + Read from PSG DTB 0 1 1 + Latch address BAR 1 0 0 + Inactive DW 1 0 1 + Write to PSG DWS 1 1 0 + Latch address INTAK 1 1 1 + ***************************************************************************/ #include "emu.h" -- cgit v1.2.3