Ports Configuration

The 8 I/O ports P0 through P7 can be configured to any

combination of inputs and outputs using the ports con-

figuration register (Table 5). The INT/O8 output can also

be configured as an extra general-purpose output

using the configuration register (Table 4).

Input Ports

The input ports register is read only (Table 6). It reflect

the incoming logic levels of the ports, regardless of

whether the port is defined as an input or an output by

the ports configuration register. Reading the input ports

register latches the current-input logic level of the

affected eight ports. A write to the input ports register is

ignored.

Transition Detection

All ports configured as inputs are always monitored for

changes in their logic status. The action of reading the

input ports register or writing to the configuration regis-

ter samples the corresponding 8 port bits’ input condi-

tion ( Tables 4, 6 ). This sample is continuously

compared with the actual input conditions. A detected

change in input condition causes an interrupt condition.

The interrupt is cleared either automatically if the

changed input returns to its original state, or when the

input ports register is read, updating the compared

data (Figure 10). Randomly changing a port from an

output to an input may cause a false interrupt to occur if

the state of the input does not match the content of the

input ports register. The interrupt status is available as

the interrupt flag INT in the configuration register (Table

4).

The input status of all ports is sampled immediately

after power-up as part of the MAX7315’s internal initial-

ization, so if all the ports are pulled to valid logic levels

at that time an interrupt does not occur at power-up.

INT

/O8 Output

The INT/O8 output pin can be configured as either the

INT output that reflects the interrupt flag logic state or as

a general-purpose output O8. When used as a general-

purpose output, the INT/O8 pin has the same blink and

PWM intensity control capabilities as the other ports.

Set the interrupt enable I bit in the configuration register

to configure INT/O8 as the INT output (Table 4). Clear

interrupt enable to configure INT/O8 as the O8. O8

logic state is set by the 2 bits O1 and O0 in the configu-

ration register. O8 follows the rules for blinking selected

by the blink enable flag E in the configuration register. If

blinking is disabled, then interrupt output control O0

alone sets the logic state of the INT/O8 pin. If blinking is

enabled, then both interrupt output controls O0 and O1

set the logic state of the INT/O8 pin according to the

blink phase. PWM intensity control for O8 is set by the 4

global intensity bits in the master, O8 intensity register

(Table 13).

Blink Mode

In blink mode, the output ports can be flipped between

using either the blink phase 0 register or the blink phase

1 register. Flip control is by software control (the blink flip

flag B in the configuration register) (Table 4). If hardware

flip control is needed, consider the MAX7316, which

includes a BLINK input, as well as software control.

The blink function can be used for LED effects by pro-

gramming different display patterns in the two sets of

8-Port I/O Expander with LED Intensity

Control, Interrupt, and Hot-Insertion Protection

______________________________________________________________________________________

13

Table 2. Register Address Map

REGISTER

ADDRESS CODE

(HEX)

AUTOINCREMENT

ADDRESS

Read input ports

0x00

0x00 (no change)

Blink phase 0 outputs

0x01

0x01 (no change)

Ports configuration

0x03

0x03 (no change)

Blink phase 1 outputs

0x09

0x09 (no change)

Master, O8 intensity

0x0E

0x0E (no change)

Configuration

0x0F

0x0F (no change)

Outputs intensity P1, P0

0x10

0x11

Outputs intensity P3, P2

0x11

0x12

Outputs intensity P5, P4

0x12

0x13

Outputs intensity P7, P6

0x13

0x10