ports register latches the current-input logic level of the

affected eight ports. Transition detection allows all

ports configured as inputs to be monitored for changes

in their logic status. The action of reading the input

ports register samples the corresponding 8 port bits’

input condition. This sample is continuously compared

with the actual input conditions. A detected change in

input condition causes the INT/O8 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 input ports reg-

ister is read.

The INT/O8 pin can be configured as either an interrupt

output or as a 9th output port with the same static or

blink controls as the other eight ports (Table 4).

Port Output Control and LED Blinking

The blink phase 0 register sets the output logic levels of

the eight ports P0–P7 (Table 8). This register controls

the port outputs if the blink function is disabled. A

duplicate register, the blink phase 1 register, is 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 register and the blink phase 1 regis-

ter using software control (the blink flip flag in the con-

figuration register) (Table 4).

PWM Intensity Control

The MAX7315 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 MAX7315 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 MAX7315

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 MAX7315 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 MAX7315 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 MAX7315 and generates the SCL clock that

synchronizes the data transfer (Figure 2).

The MAX7315 SDA line operates as both an input and

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

Ω,

is required on SDA. The MAX7315 SCL line operates

8-Port I/O Expander with LED Intensity

Control and Interrupt

_______________________________________________________________________________________

7

Figure 2. 2-Wire Serial Interface Timing Details

SCL

SDA

START

CONDITION

STOP

CONDITION

REPEATED START CONDITION

START CONDITION