Creative SB0350 Programming Manual page 83

5-8 MIDI Port I/O Programming
Reset
The command byte 0FFh is used to reset the MPU-401 interface. After resetting the
interface, a Command Acknowledge byte, 0FEh, should be read back from the Data
port.
This mechanism can also be used to detect the existence of the MPU-401 interface.
After an interface reset, the data read in from the Data port should be verified to be
0FEh. If this fails, either the MPU-401 is not installed, or it does not exist at that I/O
address.
Example code:
Busy:
Empty:
NextLoop:
mov dx,wMpuBaseAddx
inc dx
in al,dx
test al,40h
jnz Busy
mov al,0FFh
out dx,al
sub cx,cx
in al,dx
test al,80h
jnz NextLoop
dec dx
in al,dx
cmp al,0FEh
je ResetOK
inc dx
loop Empty
;***
;*** Failed to reset: MPU-401 not detected
;MPU-401 base I/O address
;Status port
;Read status port
;Ready for output?
;No
;Output "Reset" command
; via Command port
;Maximum of 65536 tries
;Read status port
;Input data ready?
;No
;Data port
;Read data
;Successfully reset?
;SUCCESS!
;Status port
;Try again