(4) Level control (controlled by R8 ~ RA)
The audio level output from the D/A convertors for the three channels (A,B
and C) is adjusted by registers R8, R9 and RA.
Level setting registers Channel
R8 A
R9 B
RA C
B7 B6 B5 B4 B3 B2 B1 B0
\------/| |\ \
Not used| | \ \
| | \ \
M L3 L2 L1 L0
Mode 4 bit level selection
Mode M selects whether the level is fixed (when M=0) or variable (M=1). When
M=0, level is determined from one of 16 by level selection signals L3,L2,L1
and L0 which compromise the lower four bits. When M=1, the level is determined
by the 5 bit output of E4,E3,E2,E1 and E0 of the envelope generator of the
SSG. (This level is variable as E4 ~ E0 change over time)
(5) Setting of envelope frequency (controlled by R8 and RC)
Thus, the envelope repetition frequency fE is obtained as follows from the
envelope setting period value EP (decimal):
fE = fMaster (fMaster if the frequency of the master clock)
-------
256EP
Envelope rough adjustment register RC Envelope fine adjustment register RB
B7 B6 B5 B4 B3 B2 B1 B0 B7 B6 B5 B4 B3 B2 B1 B0
/ \ / \
/ \ / \
/ | \
EP15 EP14 EP13 EP12 EP11 EP10 EP9 EP8 EP7 EP6 EP5 EP4 EP3 EP2 EP1 EP0
16 bit envelope period setting value (EP)
The period of the actual frequency fEA used for the envelope generated is
1/32 of the envelope repetition period (1/fE).
(6) Envelope shape control (controlled by RD)
The envelope generator counts the envelope clock fEA 32 times for each
envelope pattern cycle. The envelope level is determined by the 5 bit output
(E4 ~ E0) of the counter. The shape of the envelope is created by increasing,
decreasing, stopping, or repeating this counter. The shape is controlled by
bits B3 ~ B0 of the register RD.
Envelope shape control register RD
B7 B6 B5 B4 B3 B2 B1 B0
\----------/ | | | |
Not used | | | --- Hold
| | ------ Alt
| --------- Att
------------ Cont
Envelope shape control signals
Version: v005
23
Date: 22.05.2012
