MAX7301(2003) Ver la hoja de datos (PDF) - Maxim Integrated

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MAX7301
(Rev.:2003)

4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port I/O Expander

Maxim Integrated 

4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and

28-Port I/O Expander

CS

SCLK

DIN

tCSS

tCSH

tDS

tDH

tCH

tCL

DOUT

tCSH

tDO

Figure 2. 4-Wire Interface

Initial Power-Up

On initial power-up, all control registers are reset, and

the MAX7301 enters shutdown mode (Table 4).

Transition (Port Data Change) Detection

Port transition detection allows any combination of the

seven ports P24–P30 to be continuously monitored for

changes in their logic status (Figure 5). A detected

change is flagged on port P31, which is used as an

active-high interrupt output (INT). Note that the

MAX7301 does not identify which specific port(s)

caused the interrupt, but provides an alert that one or

more port levels have changed.

The mask register contains 7 mask bits that select

which of the seven ports, P24–P30 are to be monitored

(Table 8). Set the appropriate mask bit to enable that

port for transition detect. Clear the mask bit if transitions

on that port are to be ignored. Transition detection

works regardless of whether the port being monitored is

set to input or output, but generally it is not particularly

useful to enable transition detection for outputs.

Port P31 must be configured as an output in order to

work as the interrupt output INT when transition detec-

tion is used. Port P31 is set as output by writing bit D7

= 0 and bit D6 = 1 to the port configuration register

(Table 1).

To use transition detection, first set up the mask regis-

ter and configure port P31 as an output, as described

above. Then enable transition detection by setting the

M bit in the configuration register (Table 7). Whenever

the configuration register is written with the M bit set,

the MAX7301 updates an internal 7-bit snapshot regis-

ter, which holds the comparison copy of the logic states

of ports P24 through P30. The update action occurs

regardless of the previous state of the M bit, so that it is

not necessary to clear the M bit and then set it again to

update the snapshot register.

When the configuration register is written with the M bit

set, transition detection is enabled and remains

enabled until either the configuration register is written

with the M bit clear, or a transition is detected. The INT

output port P31 goes low, if it was not already low.

Once transition detection is enabled, the MAX7301

continuously compares the snapshot register against

the changing states of P24 through P31. If a change on

any of the monitored ports is detected, even for a short

time (like a pulse), INT output port P31 is latched high.

The INT output is not cleared if more changes occur or

if the data pattern returns to its original snapshot condi-

tion. The only way to clear INT is to access (read or

write) the transition detection mask register (Table 8).

Transition detection is a one-shot event. When INT has

been cleared after responding to a transition event,

transition detection is automatically disabled, even

though the M bit in the configuration register remains

set (unless cleared by the user). Reenable transition

detection by writing the configuration register with the

M bit set, to take a new snapshot of the seven ports

P24 to P30.

8 _______________________________________________________________________________________

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