as an input or an output. Reading an input ports regis-

ter latches the current-input logic level of the affected

eight ports. Transition detection allows all ports config-

ured as inputs to be monitored for changes in their

logic status. The action of reading an input ports regis-

ter samples the corresponding 8 port bits’ input condi-

tions. This sample is continuously compared with the

actual input conditions. A detected change in input

condition causes the INT/O16 interrupt output to go

low, if configured as an interrupt output. The interrupt is

cleared either automatically if the changed input

returns to its original state, or when the appropriate

input ports register is read.

The INT/O16 pin can be configured as either an inter-

rupt output or as a 17th output port with the same static

or blink controls as the other 16 ports (Table 4).

Port Output Control and LED Blinking

The two blink phase 0 registers set the output logic lev-

els of the 16 ports P0–P15 (Table 8). These registers

control the port outputs if the blink function is disabled.

A duplicate pair of registers, the blink phase 1 regis-

ters, are also used if the blink function is enabled

(Table 9). In blink mode, the port outputs can be

flipped between using the blink phase 0 registers and

the blink phase 1 registers using software control (the

blink flip flag in the configuration register) (Table 4).

PWM Intensity Control

The MAX7313 includes an internal oscillator, nominally

32kHz, to generate PWM timing for LED intensity con-

trol. PWM intensity control can be enabled on an out-

put-by-output basis, allowing the MAX7313 to provide

any mix of PWM LED drives and glitch-free logic out-

puts (Table 10). PWM can be disabled entirely, in

which case all output ports are static and the MAX7313

operating current is lowest because the internal oscilla-

tor is turned off.

PWM intensity control uses a 4-bit master control and 4

bits of individual control per output (Tables 13, 14). The

4-bit master control provides 16 levels of overall intensi-

ty control, which applies to all PWM-enabled output

ports. The master control sets the maximum pulse

width from 1/15 to 15/15 of the PWM time period. The

individual settings comprise a 4-bit number further

reducing the duty cycle to be from 1/16 to 15/16 of the

time window set by the master control.

For applications requiring the same PWM setting for all

output ports, a single global PWM control can be used

instead of all the individual controls to simplify the con-

trol software and provide 240 steps of intensity control

(Tables 10 and 13).

Standby Mode

When the serial interface is idle and the PWM intensity

control is unused, the MAX7313 automatically enters

standby mode. If the PWM intensity control is used, the

operating current is slightly higher because the internal

PWM oscillator is running. When the serial interface is

active, the operating current also increases because

transmission.

Serial Interface

Serial Addressing

The MAX7313 operates as a slave that sends and

face. The interface uses a serial data line (SDA) and a

serial clock line (SCL) to achieve bidirectional commu-

nication between master(s) and slave(s). A master (typ-

ically a microcontroller) initiates all data transfers to and

from the MAX7313 and generates the SCL clock that

synchronizes the data transfer (Figure 2).

The MAX7313 SDA line operates as both an input and

an open-drain output. A pullup resistor, typically 4.7k

Ω,

is required on SDA. The MAX7313 SCL line operates

16-Port I/O Expander with LED Intensity

Control, Interrupt, and Hot-Insertion Protection

_______________________________________________________________________________________

7

Figure 2. 2-Wire Serial Interface Timing Details

SCL

SDA

START

CONDITION

STOP

CONDITION

REPEATED START CONDITION

START CONDITION