
P
P
- 20 - 
 Andigilog, Inc. 2006 
www.andigilog.com
October 2006 - 70A05007 
aSC7611
Register 04-07h: Fan Tachometer Measurement Configuration 
Register 
Address 
Read/ 
Write 
Register 
Name 
Bit 7 
(MSB) 
Bit 6 
Bit 5 
Bit 4 
Bit 3 
Bit 2 
Bit 1 
Bit 0 
(LSB) 
Default 
Value 
04h 
R/W 
Tach 1 
Configuration 
3-Wire 
Enable1 
3-Wire 
Enable0 
Meas 
Blank 1 
Meas 
Blank 0 
Meas 
Dwell 1 
Meas 
Dwell 0 
Meas 
Duration 
1 
Meas 
Duration 
0 
36 
05h 
R/W 
Tach 2 
Configuration 
3-Wire 
Enable1 
3-Wire 
Enable0 
Meas 
Blank 1 
Meas 
Blank 0 
Meas 
Dwell 1 
Meas 
Dwell 0 
Meas 
Duration 
1 
Meas 
Duration 
0 
36 
06h 
R/W 
Tach 3 
Configuration 
3-Wire 
Enable1 
3-Wire 
Enable0 
Meas 
Blank 1 
Meas 
Blank 0 
Meas 
Dwell 1 
Meas 
Dwell 0 
Meas 
Duration 
1 
Meas 
Duration 
0 
36 
07h 
R/W 
Tach 4 
Configuration 
3-Wire 
Enable1 
3-Wire 
Enable0 
Meas 
Blank 1 
Meas 
Blank 0 
Meas 
Dwell 1 
Meas 
Dwell 0 
Meas 
Duration 
1 
Meas 
Duration 
0 
36 
The Fan Tachometer Configuration registers contain the settings that define the modes of measurement of the Tachometer 
input signals. The user is allowed to disable a tachometer measurement or to request PWM stretching, in the case of a 3-
wire fan. Also, the rate, start-up and period of measurements within a fan rotation cycle may be selected. The table below 
describes the controls. 
Bit 
Name 
R/W 
Default 
Description 
1:0 
Measurement 
Duration 
R/W 
10 
The amount of fan rotation used for the tach measurement. 
Assumes 2 pulse periods per rotation of fan. 
00:  Rotation – Tach Count x4 = Reported Valu 
01:  Rotation – Tach Count x2 = Reported Value 
10: 1 Rotation – Tach Count x1 = Reported Value (default) 
11: 2 Rotation – Tach Count x1 = Reported Value 
3:2 
Measurement 
Dwell 
R/W 
01 
Delay between Tach Measurements 
00: 100 ms 
01: 300 ms (default) 
10: 500 ms 
11: 728 ms 
5:4 
Measurement 
Blank 
R/W 
11 
In 3-wire fan mode, a delay is needed to assure that the tach 
input has stabilized after the PWM has been set to 100% 
00: 11.1 μs 
01: 22.2 μs 
10: 33.3 μs 
11: 44.4 μs (default) 
7:6 
3-Wire Enable 
R/W 
00 
For 3-Wire mode, the PWM output will be forced to 100% when 
the tach measurement is being processed. Each fan has a 3-
Wire Mode control that will behave as indicated in this table:  
HLFRQ 
(5Fh-61h) 
3-Wire Enable (7:6) 
3-Wire 
Mode 
0 
0 
0 
Enabled 
0 
0 
1 
Enabled 
0 
1 
0 
Enabled 
0 
1 
1 
Disabled 
1 
0 
0 
Disabled 
1 
1 
0 
1 
1 
0 
Disabled 
Enabled 
1 
1 
1 
Disabled 
Table 6 Tachometer Configuration Register