AM186EM Datasheet, PDF (33/98 Pages) List of Unclassifed Manufacturers – MICROCONTROLLER BLOCK DIAGRAM

PRELIMINARY
UZI/PIO26
Upper Zero Indicate (output, synchronous)
UZI—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, and it as-
serts in the first period of a bus cycle and is held
throughout the cycle.
This signal should be pulled High or allowed to float at
reset. If this pin is Low at the negation of reset, the
Am186EM and Am188EM microcontrollers will enter a re-
served clock test mode.
V_CC
Power Supply (input)
These pins supply power (+5 V) to the microcontroller.
WHB (Am186EM 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 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 (Am186EM Microcontroller Only)
WB (Am188EM 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 AD0 and WR. This pin floats during reset.
WB—On the Am188EM 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 floats during reset.
WR
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 floats
during a bus hold or reset condition.
X1
Crystal Input (input)
This pin and the X2 pin provide connections for a fun-
damental mode or third-overtone parallel-resonant
crystal used by the internal oscillator circuit. To provide
the microcontroller with an external clock source, con-
nect the source to the X1 pin and leave the X2 pin un-
connected.
X2
Crystal Output (output)
This pin and the X1 pin provide connections for a fun-
damental 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.
Am186/188EM and Am186/188EMLV Microcontrollers
33