Formats for Data Transfer are as follows:
FREQUENCY OPDATE (Double Byte Transfer)
FIRST BYTE SECOND BYTE
DATA
F9 F8 F7 F6
REGISTER
ADDRESS
R2 Rl RO
BIT 0
1
D7 DO
DATA
F5 F4 F3 F2 Fl FO X
3IT 0
0
D7 DO
SHIFT
NF1
NOISE
RATE
NFO
SOURCE UPDATE
FEEDBACK
FB X
(Single Byte Transfer)
REGISTER ADDRESS
R2 Rl RO
BIT 0
1
D7 DO
ATTENUATOR UPDATE (Single Byte Transfer)
DATA
A3 A2 Al AO
REGISTER ADDRESS
R2 Rl RO
BIT 0
1
D7 DO
2.5 CPU INTERFACE
Eight_U) data lines (D0-D7) and three (3) control lines
(TO,
CE, READY) interface the NCR 8496 Sound Generator to
the CPU. As indicated in Section 2.2, Tone Generation, ten
(10) bits of data are required by each tone generator in
selecting frequency values. Frequency updates require
double byte data transfers. An additional four (4) bits of
data are required to select the attenuation values.
Attenuation updates require only single byte data transfers.
(See Section 2.4: Data
Transfer).
Tone generators can be quickly updated by initially sending
both bytes of frequency and register data, followed by only
the second byte of data for succeeding values only if no
other control registers are accessed at the time of
generator updating. This action is accomplished by latching
the register address and permitting the continued transfer
of data into the same register. This updating feature
permits the expedited modification of the six (6) most
significant bits of data needed for frequency sweeps.
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