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ay8910: Handy guide to bus control signals (nw)

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AJR 2017-03-05 13:44:08 -05:00
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src/devices/sound/ay8910.cpp
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@ -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"