Creative SB0350 Hardware Programming Guide - Page 83

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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: mov inc Busy: in test jnz mov out sub Empty: in test jnz dec in cmp je inc al,dx al,80h NextLoop dx al,dx al,0FEh ResetOK dx ;Read status port ;Input data ready? ;No ;Data port ;Read data ;Successfully reset? ;SUCCESS! ;Status port al,dx al,40h Busy al,0FFh dx,al cx,cx ;Read status port ;Ready for output? ;No ;Output "Reset" command ; via Command port ;Maximum of 65536 tries dx,wMpuBaseAddx dx ;MPU-401 base I/O address ;Status port NextLoop: loop Empty ;Try again ;*** ;*** Failed to reset: MPU-401 not detected

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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:
mov
dx,wMpuBaseAddx
;MPU-401 base I/O address
inc
dx
;Status port
Busy:
in
al,dx
;Read status port
test
al,40h
;Ready for output?
jnz
Busy
;No
mov
al,0FFh
;Output "Reset" command
out
dx,al
;
via Command port
sub
cx,cx
;Maximum of 65536 tries
Empty:
in
al,dx
;Read status port
test
al,80h
;Input data ready?
jnz
NextLoop
;No
dec
dx
;Data port
in
al,dx
;Read data
cmp
al,0FEh
;Successfully reset?
je
ResetOK
;SUCCESS!
inc
dx
;Status port
NextLoop:
loop
Empty
;Try again
;***
;*** Failed to reset: MPU-401 not detected