User’s Manual
Custom Embedded Solutions
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81
OUT DX, AL
6. How to control R137 LAN bypass function by GPIO during power on state
The bypass function can be enabled or disabled through ICH GPIO33 during
power on state. Below is the I/O port address and control bit.
Power ON State Bypass Control Status Register
I/O Address: 4B8H
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
W
W
X
X
X
X
W
X
W: Write, X: Not used
Bit 1
1 – Set segment 1 bypass to disable when power on
0 – Set segment 1 bypass to enable when power on
Segment 1: Control by GPIO 33
Normal state (Behavior A)
===============================
MOV DX, 4B8H
;address
IN AX, DX
;read value
AND AL, 0FDH
;mask bit 1
OR AL, 02H
;set bit 1 = 1
OUT DX, AL
;send value
Bypass Enabled (Behavior B)
===============================
MOV DX, 4B8H
;address
IN AX, DX
;read value
AND AL, 0FDH
;mask bit 1
OR AL, 00H
;set bit 1 = 0
OUT DX, AL
;send value
