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UZI
V
CC
WHB
WLB/WB
WR
3-14
Upper Zero Indicate (output, synchronous)
This pin lets the designer determine whether 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 Am186EM and AO15–AO10 on the
Am188EM). UZI is the logical OR of the inverted A19–A16 bits, and it
asserts in the first period of a bus cycle and is held throughout the cycle.
This pin should be allowed to float or should be pulled High at reset. If
this pin is Low at the negation of reset, the Am186EM and Am188EM
microcontrollers will enter a reserved clock test mode.
Power Supply (input)
These pins supply power (+5 V) to the microcontroller.
Write High Byte, Am186EM Microcontroller Only
(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 provided by BHE, the least-significant address bit
(AD0), and by 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.
Write Low Byte, Am186EM Microcontroller Only
(output, three-state, synchronous)
Write Byte, Am188EM Microcontroller Only
(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, the least-significant
address bit (AD0), and by 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 Am188EM 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. WB
is the logical OR of WHB and WLB, which are not present on the
Am188EM microcontroller.
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.
System Overview
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