P R E L I M I N A R Y
controller does not inadvertently enter ONCE mode,
WR
ONCE1 has a weak internal pullup resistor that is ac-
tive only during a reset. This pin is not three-stated dur-
ing a bus hold condition.
Write Strobe (output, synchronous)
WR—This pin indicates to the system that the data on
the bus is to be written to a memory or I/O device. WR
floats during a bus hold or reset condition.
UZI/PIO26
Upper Zero Indicate (output, synchronous)
X1
This pin lets the designer determine if an access to the
interrupt vector table is in progress by ORing it with bits
15–10 of the address and data bus (AD15–AD10 on
the 186 and AO15–AO10 on the 188). UZI is the logical
OR of the inverted A19–A16 bits. It asserts in the first
period of a bus cycle and is held throughout the cycle.
Crystal Input (input)
This pin and the X2 pin provide connections for a
fundamental mode or third-overtone, parallel-resonant
crystal used by the internal oscillator circuit. To provide
the microcontroller with an external clock source,
connect the source to the X1 pin and leave the X2 pin
unconnected.
This pin should be allowed to float or it should be pulled
High at reset. This pin has an internal pullup. If this pin
is Low at the negation of reset, the Am186ES and
Am188ES microcontrollers will enter a reserved clock
test mode.
X2
Crystal Output (output)
This pin and the X1 pin provide connections for a
fundamental mode or third-overtone, parallel-resonant
crystal used by the internal oscillator circuit. To provide
the microcontroller with an external clock source, leave
the X2 pin unconnected and connect the source to the
X1 pin.
V
CC
Power Supply (input)
These pins supply power (+5 V) to the microcontroller.
WHB (Am186ES 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 microcontroller 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 eliminated.
WHB is asserted with AD15–AD8. WHB is the logical
OR of BHE and WR. This pin floats during reset.
WLB (Am186ES Microcontroller Only)
WB (Am188ES 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 microcontroller 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 eliminated.
WLB is asserted with AD7–AD0. WLB is the logical OR
of AD0 and WR. This pin floats during reset.
WB—On the Am188ES microcontroller, this pin
indicates a write to the bus. WB uses the same early
timing as the nonmultiplexed address bus. WB is
associated with AD7–AD0. This pin floats during reset.
Am186/188ES and Am186/188ESLV Microcontrollers
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AMD [ AMD ]
