Frogger Sound Board Hardware

AY38910 Chip

Port space addressing is straightforward. If upper address bit 7 is set, value is written to chip address register. If address bit 6 is set, value is written (or read) to chip register last addressed.

40pAY_DATARead/write the selected AY internal register
80pwAY_ADDRWrite here to select AY internal register

Capacitor Network

6000:6FFFw capsCapacitor network

There is a capacitor filter control network controlled through memory addresses decoded from 6000. Reading from an address sets the filter as follows:

Address 0110_aa_bb_cc_dd_ee_ff
aa, bb, cc are AY chip 0 voices
dd, ee, ff are AY chip 1 voices (not used in this 1-chip hardware)

For each voice the two-bit data switches capacitors as follows:
00 None
01 0.220uF
10 0.047uF
11 0.047uF + 0.220uF