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This subroutine is called with the A register holding a valid stream number - normally 253 to 3. Then depending on the stream data a particular channel will be made the current channel.
A Stream number
CHAN_OPEN 05633 ADD A,A The value in the A register is doubled and then increased by 22.
05634 ADD A,22
05636 LD L,A The result is moved to L.
05637 LD H,92 The address 23574 is the base address for stream 0.
05639 LD E,(HL) Fetch the first two bytes of the required stream's data.
05640 INC HL
05641 LD D,(HL)
05642 LD A,D Give an error if both bytes are zero; otherwise jump forward.
05643 OR E
05644 JR NZ,CHAN_OP_1
This entry point is used by the routine at STR_ALTER.
Report O - Invalid stream.
REPORT_O 05646 RST 8 Call the error handling routine.
05647 DEFB 23
Using the stream data now find the base address of the channel information associated with that stream.
CHAN_OP_1 05648 DEC DE Reduce the stream data.
05649 LD HL,(23631) The base address of the whole channel information area (CHANS).
05652 ADD HL,DE Form the required address in this area.
This routine continues into CHAN_FLAG.
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