AM186 datasheet(39/112 Pages) AMD

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Am186TMER and Am188TMER Microcontrollers Data Sheet

DRAF

Table 6.

Clocking Modes

VCC

Power Supply (input)

These pins supply power (+3.3 V) to the microcontrol-

ler.

WHB (Am186™ER Microcontroller Only)

Write High Byte (output, three-state, synchronous)

This pin and WLB indicate to the system which bytes of

the data bus (upper, lower, or both) participate in a

write cycle. In 80C186 designs, this information is pro-

vided by BHE, AD0, and WR. However, by using WHB

and WLB, the standard system interface logic and ex-

ternal address latch that were required are eliminated.

WHB is asserted with AD15–AD8. WHB is the logical

OR of BHE and WR. During reset, this pin is a pullup.

This pin is three-stated during bus holds and ONCE

mode.

WLB (Am186™ER Microcontroller Only)

WB (Am188™ER Microcontroller Only)

Write Low Byte (output, three-state, synchronous)

Write Byte (output, three-state, synchronous)

WLB—This pin and WHB indicate to the system which

bytes of the data bus (upper, lower, or both) participate

in a write cycle. In 80C186 designs, this information is

provided by BHE, AD0, and WR. However, by using

WHB and WLB, the standard system interface logic

and external address latch that were required are elim-

inated.

WLB is asserted with AD7–AD0. WLB is the logical OR

of A0 and WR. This pin is three-stated during bus holds

and ONCE mode.

WB—On the Am188ER microcontroller, this pin indi-

cates a write to the bus. WB uses the same early timing

as the nonmultiplexed address bus. WB is associated

with AD7–AD0. This pin is three-stated during bus

holds and ONCE mode.

Write Strobe (output, synchronous)

This pin indicates to the system that the data on the bus

is to be written to a memory or I/O device. WR is three-

stated during a bus hold or reset condition.

Crystal Input (input)

This pin and the X2 pin provide connections for a fun-

damental mode crystal used by the internal oscillator

circuit. If providing an external clock source, connect

the source to X1 and leave X2 unconnected. Unlike the

rest of the pins on the Am186ER and Am188ER micro-

controllers, X1 is not 5-V tolerant and has a maximum

input equal to VCC.

Crystal Output (output)

This pin and the X1 pin provide connections for a fun-

damental mode crystal used by the internal oscillator

circuit. If providing an external clock source, connect

the source to X1 and leave X2 unconnected. Unlike the

rest of the pins on the Am186ER and Am188ER micro-

controllers, X2 is not 5-V tolerant.

CLKSEL2CLKSEL1

Clocking Mode

Times Four

Divide by Two

Times One

Reserved1

Notes:

1. The reserved clocking mode should not be used. Entering

the reserved clocking mode may cause unpredictable

system behavior.

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