MIC74_14 Datasheet, PDF (7/20 Pages) Micrel Semiconductor – 2-Wire Serial I/O Expander and Fan Controller

Micrel, Inc.
MIC74
Register Descriptions (Continued)
Table 6. Data Register
DATA
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
P7
P6
P5
P4
Data Register Parameters
• Power-on default value: 1111 1111_b, FF_h
• Command_byte address: 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.
P3
P2
P1
P0
• Read operation: 1 = Pn is high; 0 = Pn is low
• Write operation: 1 = Pn is set to ‘1’; 0 = Pn is cleared
• Notes: If the FAN bit of the DEV_CFG register is set to
‘1’ (i.e., if fan mode is selected), 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 determined by the FAN_SPEED
register. While in fan mode, D[7:4] of the DATA
registers have no effect.
Table 7. 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 Register Parameters
• Power-on default value: 0000 0000_b, 00_h
− Fan off
• Command_byte address: 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: Fan speed settings (see below)
Fan Speed
• Notes: Any time the fan speed register contains zero,
meaning 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 (tSTART).
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.
D[2:0]
Value
Output State
/FS[2:0]
/SHDN
Fan Speed
• Bit Name: D[3] through D[7]
• Function: Reserved
000
111
0
Off
• Operation: Always write as zero
001
110
1
Speed 1
(slowest)
010
101
1
Speed 2
011
100
1
Speed 3
100
011
1
Speed 4
101
010
1
Speed 5
110
001
1
Speed 6
111
000
1
Speed 7
(fastest)
September 30, 2014
7
Revision 3.0