Specifications

4-2 Mixer Chip Programming
Programming Sequence
Each mixer chip uses two consecutive I/O ports: 2x4h and 2x5h where x depends on
the jumper selectable setting of the base I/O address. Port 2x4h is the write-only
Address Port. Port 2x5h is the Data Port which can be read or written.
The sequence for programming a mixer chip is as follows:
1. write the index of the mixer register to the Address Port.
2. write/read the mixer register value to/from the Data Port.
The following assembly code fragment shows the process of accessing a mixer
register:
; Common setup code
; Specify which register to access
;
mov dx,wSBCBaseAddx ; Base I/O address
add dx,4 ; Mixer address port
mov al,bMixerRegIndex ; Index of mixer's register
out dx,al ; Select the register
inc dx ; Mixer data port
; Write to the mixer register
;
mov al,bMixerRegSetting ; Set the register setting
out dx,al
; Read from the mixer register
;
mov al,bMixerRegSetting ; Retrieve the register setting
in al,dx