CFA633-RDI-KS datasheet(52/88 Pages) CRYSTAIFONTZ

52 / 88 page

Crystalfontz America, Inc.

Data Sheet Release Date 2012/02/21

www.crystalfontz.com

CFA633-RDI-KS LCD Module (Hardware v2.0 / Firmware s2v1)

February 2012

Page 52

Varying fan speeds under host software control gives the ultimate flexibility in system design but would typically have a

fatal flaw: a host software or hardware failure could cause the cooling system to fail. If the fans were set at a slow speed

when the host software failed, system components may be damaged due to inadequate cooling.

The fan power fail-safe command allows host control of the fans without compromising safety. When the fan control

software activates, it should set the fans that are under its control to fail-safe mode with an appropriate timeout value. If

for any reason the host fails to update the power of the fans before the timeout expires, the fans previously set to fail-

safe mode will be forced to 100% power.

#define FAN_1

0x01

#define FAN_2

0x02

#define FAN_3

0x04

#define FAN_4

0x08

type = 0x19 = 2510

data_length = 2

data[0] = bit mask of fans set to fail-safe (1-15 valid)

data[1] = timeout value in 1/8 second ticks:

1 = 1/8 second

2 = 1/4 second

255 = 31 7/8 seconds

The return packet will be:

type = 0x40 | 0x19 = 0x59 = 8910

data_length = 0

26 (0x1A): Set Fan Tachometer Glitch Filter

The CFA633 controls fan speed by using PWM. Using PWM turns the power to a fan on and off quickly to change the

average power delivered to the fan. The CFA633 uses approximately 18 Hz for the PWM repetition rate. The fan’s

tachometer output is only valid if power is applied to the fan. Most fans produce a valid tachometer output very quickly

after the fan has been turned back on but some fans take time after being turned on before their tachometer output is

valid.

This command allows you to set a variable-length delay after the fan has been turned on before the CFA633 will

recognize transitions on the tachometer line. The delay is specified in counts, each count being nominally 552.5 µS long

(1/100 of one period of the 18 Hz PWM repetition rate).

In practice, most fans will not need the delay to be changed from the default length of 1 count. If a fan’s tachometer output

is not stable when its PWM setting is other than 100%, simply increase the delay until the reading is stable. Typically you

would (1) start at a delay count of 50 or 100, (2) reduce it until the problem reappears, and then (3) slightly increase the

delay count to give it some margin.

Setting the glitch delay to higher values will make the RPM monitoring slightly more intrusive at low power settings. Also,

the higher values will increase the lowest speed that a fan with RPM reporting enabled will seek at 0% power setting.

The Fan Glitch Delay is one of the items stored by the command 4 (0x04): Store Current State As Boot State (Pg. 39).

type = 0x1A = 2610

data_length = 4

data[0] = delay count of fan 1

data[1] = delay count of fan 2

data[2] = delay count of fan 3

data[3] = delay count of fan 4

The return packet will be:

type = 0x40 | 0x1A = 0x5A = 9010

data_length = 0

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