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author AJR <ajrhacker@users.noreply.github.com>2017-03-05 13:44:08 -0500
committer AJR <ajrhacker@users.noreply.github.com>2017-03-05 13:44:20 -0500
commitd4fb17a901af26c8851fdc0cbb66d54177176de7 (patch)
treee9059e548e7d3d3baab0c80e11335dc9ab2563f7
parent7a2c159724e7696c42b0480bf6b1e7bdd20a8e05 (diff)
ay8910: Handy guide to bus control signals (nw)
-rw-r--r--src/devices/sound/ay8910.cpp22
1 files changed, 22 insertions, 0 deletions
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"