WR

 

Write Strobe (output, synchronous)

 

 

 

—This pin indicates to the system that the data on the bus is to be

 

 

WR

 

 

written to a memory or I/O device.

WR

is three-stated during a bus hold

 

or reset condition.

X1

Crystal Input (input)

 

This pin and the X2 pin provide connections for a fundamental mode

 

crystal used by the internal oscillator circuit. If providing an external

 

clock source, connect the source to X1 and ground X2. Unlike the rest

 

of the pins on the Am186ER and Am188ER microcontrollers, X1 is not

 

5-V tolerant and has a maximum input equal to VCC.

X2

 

Crystal Output (output)

 

This pin and the X1 pin provide connections for a fundamental mode

crystal used by the internal oscillator circuit. If providing an external clock source, connect the source to X1 and ground X2. Unlike the rest of the pins on the Am186ER and Am188ER microcontrollers, X2 is not 5-V tolerant and has a maximum input equal to VCC.

3.1.1Pins That Are Used by Emulators

The following pins are used by emulators: A19–A0, AO15–AO8, AD7–AD0, ALE, BHE/ ADEN (on the Am186ER microcontroller), CLKOUTA, RFSH2/ADEN (on the Am188ER microcontroller), RD, S2, S1/IMDIS, S0/SREN, S6/CLKSEL1, and UZI/CLKSEL2.

Emulators require that S6/CLKSEL1 and UZI/CLKSEL2 be configured in their normal functionality, that is, as S6 and UZI.

If BHE/ADEN (on the Am186ER microcontroller) or RFSH2/ADEN (on the Am188ER microcontroller) is held Low during the rising edge of RES, S6 and UZI are configured in their normal functionality, instead of as PIOs, at reset.

System Overview

3-17

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Image 49
AMD Am188TMER, Am186TMER user manual Pins That Are Used by Emulators