MIC74_06 Datasheet, PDF (7/18 Pages) Micrel Semiconductor – 2-Wire Serial I/O Expander and Fan Controller

Micrel, Inc.
Functional Diagram
MIC74
INTn
IMn
STATUSn
STATUS_READn
DATAn
(INPUT)
OUT_CFGn
QS
QR
EDGE
DETECT
V_DD
DIRn
DATAn
(OUTPUT)
Pn (typical I/O port)
GND
Typical I/O Port (Fan Speed Control Logic Not Shown)
Functional Description
Pin Descriptions
VDD
Power supply input connection. See “Operating Ratings.”
GND
Ground or return connection for all MIC74 functions.
CLK
An CLK signal is provided by the host (master) and is
common to all devices on the bus. The CLK signal
controls all transactions in both directions on the bus and
is applied to each MIC74 at the CLK pin.
DATA
Serial data is bidirectional and is common to all devices
on the bus. The MIC74’s DATA output is open-drain.
The DATA line requires one external pull-up resistor or
current source per system that can be located anywhere
along the line.
A2, A1, A0
An MIC74 responds to its own unique address which is
assigned using the A0–A2 pins. A0–A2 set the three
LSBs (least significant bits) of the MIC74’s 7-bit slave
address. The three address pins allow eight unique
MIC74 addresses in a system. When the MIC74’s
address matches an address received in the serial bit
stream, communication is initiated.
A2, A1 and A0 should be connected to GND or VDD.
The state of these pins is sampled only once at device
power-on. New slave addresses are not accepted unless
the MIC74 is powered off then on.
Inputs
MIC74 Slave Address
A2 A1 A0
Bianary
Hex
000
010 0000_b
20_h
001
010 0001_b
21_h
010
010 0010_b
22_h
011
010 0011_b
23_h
100
010 0100_b
24_h
101
010 0101_b
25_h
110
010 0110_b
26_h
111
010 0111_b
27_h
Table 1. MIC74 Address Configuration
Alert Response Address
The MIC74 also responds to the ARA (Alert Response
Address). The ARA is used by the master (host) to
request the address of a slave that has provided an
interrupt to the master via the /ALERT line.
The ARA is a single address (0001 100) common to all
slaves and is described in more detail under “Interrupt
Generation” with related information under “/ALERT.”
Also see Figure 7.
October 2006
7
M9999-101006