MIC74BQS Micrel Inc, MIC74BQS Datasheet - Page 13

• Manufacturer Part Number: MIC74BQS
• Description: IC I/O EXPANDER I2C 8B 16QSOP
• Manufacturer: Micrel Inc
• Series: -r

Specifications of MIC74BQS

• Interface: I²C, SMBus
• Number Of I /o: 8
• Interrupt Output: Yes
• Frequency - Clock: -
• Voltage - Supply: 2.7 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.154", 3.90mm Width)
• Includes: -
• Lead Free Status / Rohs Status: Contains lead / RoHS non-compliant

Initializing the MIC74
The MIC74’s internal registers are reset to their default
state at power-on. The MIC74’s default state can be
summarized as follows:
The result of this configuration is that all I/O pins will
essentially float unless driven by external circuitry. Any
system using the MIC74 will need to initialize the internal
registers to the state required for proper system
operation. The recommended order for initializing the
MIC74’s registers is as follows:
Micrel, Inc.
October 2006
Figure 9a. Initializing the MIC74 for Polled Operation
•
•
•
•
•
All I/O’s configured as inputs (DIR = 00h)
Output configuration set to open-
drain(OUT_CFG = 00h)
All outputs high/floating (DATA = FFh)
Fan functions disabled (FAN_SPEED =
00h,FAN bit of DEV_CFG = 0)
All interrupts masked (IE bit of DEV_CFG = 0)
Set output configuration
FAN_SPEED (if using)
outputs by writing DIR
Set initial fan speed in
Write desired output
turn on fan (if using)
Set desired I/O's as
Write DEV_CFG to
values to DATA
Read STATUS
in OUT_CFG
Initialization
Initialize for
to clear it
complete
polling
13
At the conclusion of step three, any I/O’s configured as
outputs in step two will be driven to the levels
programmed into the data register in step one. The order
of step 1 through step 3 is important to insure that
spurious data does not appear at the I/O’s during
configuration. Following step 7, programming the device
configuration register, the MIC74 will begin generating
interrupts if they are enabled, and the fan will be started
if FAN_SPEED contains a nonzero value. The corresp-
onddding interrupt service routines (if any) must be
initialized and enabled prior to step seven. STATUS
should be cleared (step 6) in both polled and interrupt
driven systems.
1. Write DATA
2. Write OUT_CFG
3. Write DIR
4. Write FAN_SPEED (if using fan mode)
5. Write INT_MASK (if using interrupts)
6. Read STATUS to clear it.
7. Write DEV_CFG to enable fan mode and/or
Figure 9b. Initializing the MIC74 for Interrupts
interrupts, if using
Set output configuration
FAN_SPEED (if using)
outputs by writing DIR
Set initial fan speed in
Write INT_MASK to
Write desired ouput
Set desired I/O's as
Write DEV_CFG to
Read STATUS to
turn on interrupts
enable interrupts
and fan (if using)
values to DATA
in OUT_CFG
Initialization
Initialize for
interrupts
complete
(if using)
clear it
M9999-101006
MIC74