AM186 Datasheet, PDF (39/112 Pages) Advanced Micro Devices – High-Performance, 80C186- and 80C188-Compatible, 16-Bit Embedded Microcontrollers with RAM

WR
Table 6. Clocking Modes
Write Strobe (output, synchronous)
CLKSEL2
H
CLKSEL1
H
Clocking Mode
Times Four
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.
H
L
Divide by Two
X1
L
H
Times One
L
L
Reserved¹
Crystal Input (input)
This pin and the X2 pin provide connections for a fun-
Notes:
damental mode crystal used by the internal oscillator
1. The reserved clocking mode should not be used. Entering
the reserved clocking mode may cause unpredictable
system behavior.
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
V_CC
input equal to V_CC.
X2
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)
T ^{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
F ^{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
A _mode.
WLB (Am186™ER Microcontroller Only)
WB (Am188™ER Microcontroller Only)
Write Low Byte (output, three-state, synchronous)
R _{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
D ^{in a write cycle. In 80C186 designs, this information is}
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.
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.
Am186^TMER and Am188^TMER Microcontrollers Data Sheet
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