MIC74 Datasheet, PDF (6/20 Pages) Micrel Semiconductor – 2-Wire Serial I/O Expander and Fan Controller Advance Information

MIC74
Micrel
Interrupt Mask Register
INT_MASK
D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0]
IM7 IM6 IM5 IM4 IM3 IM2 IM1 IM0
Power-On Default Value: 0000 0000_b, 00_h
Command_byte addess: 0000 0100_b, 04_h
Type:
8-bits, read/write
Bit Name: IMn
Function: Interrupt enable bit for Pn when Pn is config-
ured as an input
Operation: 1 = enabled
0 = disabled
Notes:
If Fan Mode is selected, that is, the FAN bit of
the DEV_CFG register is set to one, P[7:4] are
automatically configured as open-drain
outputs. They are then referred to as /FS[2:0]
and /SHDN. No interrupts of any kind are
generated by these pins while in Fan Mode.
Data Register
DATA
D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0]
P7 P6 P5 P4 P3 P2 P1 P0
Power-On Default Value: 1111 1111_b, FF_h
Command_byte addess: 0000 0101_b, 05_h
Type:
8-bits, read/write
Bit Name: Pn
Function:
Returns the current state of any Pn configured
as an input and the last value written to Pn’s
configured as outputs; Writing the DATA
register sets the output state of any Pn’s
configured as outputs; writes to I/O bits
configured as inputs are ignored.
Read Operation: 1 = Pn is high
0 = Pn is low
Write Operation: 1 = Pn is set to one
0 = Pn is cleared
Notes:
If Fan Mode is selected, that is, the FAN bit of
the DEV_CFG register is set to one, P[7:4] are
automatically configured as open-drain
outputs. They are then referred to as /FS[2:0]
and /SHDN. The state of these pins is deter-
mined by the FAN_SPEED register. While in
Fan Mode, D[7:4] of the DATA registers have
no effect.
Fan Speed Register
FAN_SPEED
D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0]
Always write as zero.
Fan Speed
Power-On Default Value: 0000 0000_b, 00_h
fan off
Command_byte addess: 0000 0110_b, 06_h
Type:
8-bits, read/write
Bit Name: D[0] through D[2]
Function: Determines bit-pattern on FS[2:0]
Operation:
D[2:0]
Value
000
001
010
011
100
101
110
111
Output State
/FS[2:0]
/SHDN
111
0
110
1
101
1
100
1
011
1
010
1
001
1
000
1
Fan Speed
off
speed 1 (slowest)
speed 2
speed 3
speed 4
speed 5
speed 6
speed 7 (fastest)
Fan Speed Settings
Notes:
Any time the fan speed register contains zero,
that is, the fan is shut down, and a non-zero
value is written into the fan speed register, the
/FS[2:0] and /SHDN outputs will assume the
highest fan speed state for approximately one
second (t_START). Following this interval, the
state of the fan speed control outputs will
assume the value indicated by the contents of
FAN_SPEED. This insures that the fan will
start reliably when low speed operation is
desired.
Bit Name: D[3] through D[7]
Function: Reserved
Operation: Always write as zero.
MIC74
6
August 1, 2000