If 'Mode' = 1, the EG is used instead of the 4bit volume value.
f = 8M / (Coarse*256 + Fine) ?
Timers
Address (Z80 port 4)
Data (Z80 port 5)
$24
Bit
7
6
5
4
3
2
1
0
Def
TA counter load bits 9-2
$25
Bit
7
6
5
4
3
2
1
0
Def
-
TA counter load bits 1-0
$26
Bit
7
6
5
4
3
2
1
0
Def
TB counter load bits 0-7
$27
Bit
7
6
5
4
3
2
1
0
Def
CSM Mode
3 slot mode
Reset TB flag
Reset TA flag
Enable TB IRQ
Enable TA IRQ
Load TB
Load TA
TA = Timer A, TB = Timer B
Timers will tick until they have reached zero, at which point an IRQ will be generated if enabled. Reading port $04 will show which timer caused it.
The actual timer counter registers are not directly accessable. They can be reset to zero or initialised from load registers $24-$26
Writing 0 to the load bits in register $27 will reset the timer counter registers to zero
Writing 1 to the load bits will copy the respective timer load register to the timer counter. This only works when the timer is at zero.
When a timer expires, it is automatically reloaded from the load registers and continues.
Timer flag reset refers to the same flags that are read from port $04
CSM mode is for automatic key on for operators on the second FM channel when timer A expires?
FM part
ADPCM-A part
'Dump' in register $00 is the key on/off bit. Write 0 to start playing specified channels and write 1 to stop playing.
Address (Z80 port 6)
Data (Z80 port 7)
$00
Bit
7
6
5
4
3
2
1
0
Def
Dump
-
CH6 ON
CH5 ON
CH4 ON
CH3 ON
CH2 ON
CH1 ON
$01
Bit
7
6
5
4
3
2
1
0
Def
-
Master volume
$08~$0D (one for each channel)
Bit
7
6
5
4
3
2
1
0
Def
L
R
-
Channel volume
$10~$15 (one for each channel)
Bit
7
6
5
4
3
2
1
0
Def
Sample's start address/256 LSB
$18~$1D (one for each channel)
Bit
7
6
5
4
3
2
1
0
Def
Sample's start address/256 MSB
$20~$25 (one for each channel)
Bit
7
6
5
4
3
2
1
0
Def
Sample's stop address/256 LSB
$28~$2D (one for each channel)
Bit
7
6
5
4
3
2
1
0
Def
Sample's stop address/256 MSB
ADPCM-B part
Address (Z80 port 4)
Data (Z80 port 5)
$10
Bit
7
6
5
4
3
2
1
0
Def
Start
-
Repeat
-
Reset
$11
Bit
7
6
5
4
3
2
1
0
Def
L
R
-
$12
Bit
7
6
5
4
3
2
1
0
Def
Sample's start address/256 LSB
$13
Bit
7
6
5
4
3
2
1
0
Def
Sample's start address/256 MSB
$14
Bit
7
6
5
4
3
2
1
0
Def
Sample's stop address/256 LSB
$15
Bit
7
6
5
4
3
2
1
0
Def
Sample's stop address/256 MSB
$19
Bit
7
6
5
4
3
2
1
0
Def
Delta-N (L)
Determines sample playback rate
$1A
Bit
7
6
5
4
3
2
1
0
Def
Delta-N (H)
$1B
Bit
7
6
5
4
3
2
1
0
Def
ADPCM-B channel volume
$1C
Bit
7
6
5
4
3
2
1
0
Def
B
-
A6
A5
A4
A3
A2
A1
ADPCM-A & B channels flag control
Datasheet states playback formula as F=[Delta-N / 256] x 55.5KHz (correct?)
Write to flag control to reset/mask channel end flags
Write 1 to reset and/or mask selected flag
Write 0 to unmask selected flag
Masking a flag will prevent it from being raised when a channel sample reach its end, this means you have to write 1, then 0 to clear a flag and keep it active.
Flags must be manually cleared, playing a new sample on the channel won't clear it.
Reading
The only writable registers that can also be read are from the SSG. All other ports and addresses return different data.
Z80 port #
Data
Notes
$04
Bit
7
6
5
4
3
2
1
0
Def
Busy
-
Timer B flag
Timer A flag
When a timer expires and IRQ is enabled for the timer, the respective bit is set
$05
Bit
7
6
5
4
3
2
1
0
Def
SSG register data
Attempting to read non-SSG registers will fail
$06
Bit
7
6
5
4
3
2
1
0
Def
ADPCM-B end
-
CH6 end
CH5 end
CH4 end
CH3 end
CH2 end
CH1 end
When a channel has reached the end address and stops, the respective bit is set, unless masked
