AMSTRAD CPC464, Руководство пользователя

Страница: 120 / 249

6.10 Sound generation command sequence
Form of the command:
S O U N D G , H , I , J , K , L , M
Where....
G: Channel Status
H: Tone Period
I: Duration
J: Volume
K: Volume Envelope
L: Tone Envelope
M: Noise Period
SOUND
is a command where the parameters G to M are all integers and only the first two are
mandatory. The remaining parameters are optional, but have default values that will be discussed
under the parameter descriptions.
6.10.1 Parameter descriptions:
G: Channel Status
Value range 1.....255
default if omitted: none <mandatory entry>
In the CPC464 it is possible to play up to three different SOUNDs at once. This is achieved by
having three SOUND channels (or queues), referred to as A, B and C. The input integer range is
given in decimal form, but when converted to an 8 bit value (thus yielding a bit significant result),
the active bits specify the following commands:
DECIMAL BIT COMMAND
1 0 LSB send SOUND to channel A
2 1 send SOUND to channel B
4 2 send SOUND to channel C
8 3 rendezvous with channel A
16 4 rendezvous with channel B
32 5 rendezvous with channel C
64 6 hold
128 7 MSB flush
(LSB and
MSB
signify Least Significant Bit, and Most Significant Bit in the table above.)
integer entry examples:
2
= send the following SOUND to output channel B
5 = send the following SOUND to output channels A and C
98 = 64 + 32 + 2
= send the following SOUND to output channel B, rendezvous with channel
C and hold.
It is important to remember that if a rendezvous is to be arranged between two (or more) channels,
then it is necessary to flag on the channel status) of each channel at the appropriate time.
The hold on any combination of channels, stops the processing of that command and freezes the
queue behind it, until it is freed by a RELEASE command (or ‘flushed by a later SOUND command).