MAX7317 Maxim, MAX7317 Datasheet - Page 5

• Manufacturer Part Number: MAX7317
• Description: The MAX7317 serial-interfaced peripheral provides microprocessors with 10 I/O ports rated to 7V
• Manufacturer: Maxim

The MAX7317 is a general-purpose input/output (GPIO)
peripheral that provides 10 I/O ports, P0 to P9, con-
trolled through a high-speed SPI-compatible serial
interface. The 10 I/O ports can be used as inputs or
open-drain outputs in any combination. Ports withstand
7V independent of the MAX7317’s supply voltage
whether used as inputs or outputs.
Figure 1 shows the I/O port structure of the MAX7317.
The MAX7317 contains 10 internal registers, addressed
as 0x00–0x09, which control the peripheral (Table 2).
Two further addresses, 0x0E and 0x0F, do not store
data but return the port input status when read. Four
virtual addresses, 0x0A–0x0D, allow more than one
register to be written with the same data to simplify soft-
ware. The RAM register provides 1 byte of memory that
can be used for any purpose. The no-op address,
0x20, causes no action when written or read, and is
used as a dummy register when accessing one
MAX7317 out of multiple cascaded devices.
On power-up, all control registers are reset (Table 2).
Power-up status sets I/O ports P0 to P9 high imped-
ance, and puts the device into shutdown mode.
The RAM register provides a byte of memory that can
be used for any purpose.
The 10 I/O ports P0 through P9 can be configured to
any combination of inputs and outputs. Ports withstand
7V independent of the MAX7317’s supply voltage,
whether used as inputs or outputs. Configure a port as
an input by setting its output register to 0x01, which
sets the port output high impedance (Table 4).
Reading an input port register returns the logic levels at
the I/O port pins. The input port registers are read only.
A write to an input port register is ignored.
The MAX7317 uses one 8-bit register to control each
output port (Table 4). Each port can be configured as
an input or open-drain output. Write 0x00 to the output
register to set the port as a logic-low output, or 0x01 to
set the port as a logic-high output or logic input.
The 10 registers, 0x00 through 0x09, control an I/O port
each (Table 4). Four pseudo-register addresses, 0x0A
through 0x0D, allow groups of outputs to be set to the
GPIO Port Direction Configuration
Overvoltage and Hot-Insertion Protection
10-Port SPI-Interfaced I/O Expander with
_______________________________________________________________________________________
Detailed Description
Input Port Registers
Register Structure
Output Registers
RAM Register
Initial Power-Up
same value with a single command by writing the same
data to multiple output registers.
The MAX7317 communicates through an SPI-compati-
ble 4-wire serial interface. The interface has three
inputs: clock (SCLK), chip select
(DIN), and one output, data out (DOUT). CS must be
low to clock data into or out of the device, and DIN
must be stable when sampled on the rising edge of
SCLK. DOUT is stable on the rising edge of SCLK.
SCLK and DIN can be used to transmit data to other
peripherals. The MAX7317 ignores all activity on SCLK
and DIN except when CS is low.
Note that the SPI protocol expects DOUT to be high
impedance when the MAX7317 is not being accessed;
DOUT on the MAX7317 is never high impedance. Go to
www.maxim-ic.com/an1879 for ways to convert the
MAX7317 to tri-state, if required.
Controlling the MAX7317 requires sending a 16-bit
word. The first byte, D15 through D8, is the command,
and the second byte, D7 through D0, is the data byte
(Table 5).
Figure 1. Simplified Schematic of I/O Ports
SHIFT REGISTER
WRITE PULSE
READ PULSE
DATA FROM
CK
D
CK
D
PORT REGISTER
PORT REGISTER
Control and Operation Using
OUTPUT
INPUT
FF
FF
Q
Q
Q
Q
the 4-Wire Interface
Serial Interface
INPUT PORT
REGISTER DATA
OUTPUT PORT
REGISTER DATA
(CS), and data in
GND
N
I/O PIN
5