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2015-07-0038

PT0535-4

8/18/15

8

PI4MSD5V9543B

2 Channel I2C bus switch

with Interrupt Logic and Reset

Interrupt handling

The PI4MSD5V9543B provides 2 interrupt inputs, one for each channel, and one open-drain interrupt output.

When an interrupt is generated by any device, it will be detected by the PI4MSD5V9543B and the interrupt output will

be driven LOW. The channel need not be active for detection of the interrupt. A bit is also set in the control register.

Bit 4 and bit 5 of the control register corresponds to the INT0 and INT1 inputs of the PI4MSD5V9543B,

respectively. Therefore, if an interrupt is generated by any device connected to channel 1, the state of the interrupt

inputs is loaded into the control register when a read is accomplished. Likewise, an interrupt on any device connected

to channel 0 would cause bit 4 of the control register to be set on the read. The master can then address the

PI4MSD5V9543B and read the contents of the control register to determine which channel contains the device

generating the interrupt. The master can then reconfigure the PI4MSD5V9543B to select this channel, and locate the

device generating the interrupt and clear it.

It should be noted that more than one device can provide an interrupt on a channel, so it is up to the master to

ensure that all devices on a channel are interrogated for an interrupt.The interrupt inputs may be used as general-

purpose inputs if the interrupt function is not required.

If unused, interrupt inputs must be connected to VCC through a pull-up resistor.

D7

D6

INT1

INT0

D3

D2

B1

B0

Command

0

0

X

0

X

X

X

X

no interrupt on channel 0

1

interrupt on channel 0

0

0

0

X

X

X

X

X

no interrupt on channel 1

1

interrupt on channel 1

Control register read — interrupt

The Reset Pin

The RESET input is an active LOW signal which may be used to recover from a bus fault condition. By asserting

this signal LOW for a minimum of tw(rst)L, the PI4MSD5V9543B will reset its registers and I2C-bus state machine

and will deselect all channels. The RESET input must be connected to VCC through a pull-up resistor.

Power-on reset

When power is applied to VCC, an internal Power-On Reset (POR) holds the PI4MSD5V9543B in a reset

condition until VCC has reached VPOR. At this point, the reset condition is released and the PI4MSD5V9543B

registers and I2C-bus state machine are initialized to their default states (all zeroes), causing all the channels to be

deselected. Thereafter, VCC must be lowered below 0.2 V for at least 5 us in order to reset the device.