USB2227 datasheet(12/25 Pages) MICROCHIP

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USB2227/USB2228

DS00002256A-page 12

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MA[1:0]/CLK_SE

L[1:0]

117

116

I/O8PD

Memory Address Bus:

MA[1:0], These signals address memory locations within the

external memory.

SEL[1:0]. During nRESET assertion, these pins will select the

operating frequency of the external clock, and the corresponding

weak pull-down resistors are enabled. When nRESET is negated,

the value on these pins will be internal latched and these pins will

revert to MA[1:0] functionality, the internal pull-downs will be

disabled.

SEL[1:0] = ‘00’. 24MHz

SEL[1:0] = ‘01’. RESERVED

SEL[1:0] = ‘10’. RESERVED

SEL[1:0] = ‘11’. 48MHz

Note:

If the latched value is ‘1’, then the corresponding MA

pin is tri-stated when the following conditions are true:

1. IDLE bit (PCON.0) is 1.

2. INT2 is negated

3. SLEEP bit of CLOCK_SEL is 1.

If the latched value is ‘0’, then the corresponding MA pin will

function identically to the MA[15:3] pins at all times (other than

during nRESET assertion).

nMWR

Memory Write Strobe:

Program Memory Write; active low

nMRD

Memory Read Strobe:

Program Memory Read; active low

nMCE

Memory Chip Enable:

Program Memory Chip Enable; active low.

This signal is asserted, when any of the following conditions are

no longer met:

1. IDLE bit (PCON.0) is 1.

2. INT2 is negated

3. SLEEP bit of CLOCK_SEL is 1.

Note:

This signal is held to a logic ‘high’ while nRESET is

asserted.

MISC

GPIO1

114

I/O8

General Purpose I/O:

This pin may be used either as input, edge sensitive interrupt

input, or output.

GPIO2

113

I/O8

General Purpose I/O:

This pin may be used either as input, edge sensitive interrupt

input, or output.

GPIO3

I/O8

General Purpose I/O:

This pin may be used either as input, edge sensitive interrupt

input, or output.

GPIO4

111

I/O8

General Purpose I/O:

This pin may be used either as input, edge sensitive interrupt

input, or output.

Symbol

128-Pin

VTQFP

Buffer Type

Description

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