P R E L I M I N A R Y
microcontroller, tie SRDY High. If the system does not
use SRDY, tie the pin Low to yield control to ARDY.
UCS/ONCE1
Upper Memory Chip Select (output, synchronous)
ONCE Mode Request 1 (input, internal pullup)
TMRIN0/PIO11
UCS—This pin indicates to the system that a memory
access is in progress to the upper memory block. The
base address and size of the upper memory block are
programmable up to 512 Kbytes.
Timer Input 0 (input, synchronous, edge-sensitive)
This pin supplies a clock or control signal to the internal
microcontroller timer 0. After internally synchronizing a
Low-to-High transition on TMRIN0, the microcontroller
increments the timer. TMRIN0 must be tied High if not
being used. When PIO11 is enabled, TMRIN0 is pulled
High internally.
UCS is three-stated and held resistively High during a
bus hold condition. In addition, UCS has an ~9-kohm
internal pullup resistor that is active during reset.
TMRIN0 is driven internally by INT2/INTA0/PWD when
pulse width demodulation mode is enabled. The
TMRIN0/PIO11 pin can be used as a PIO when pulse
width demodulation mode is enabled.
After reset, UCS is active for the 64 Kbyte memory
range from F0000h to FFFFFh, including the reset
address of FFFF0h.
When RAS1 is activated, the code activating RAS1
must not reside in the UCS memory block. When RAS1
is activated, UCS is automatically deactivated and
remains negated. This allows code to boot from UCS,
copy its code to another memory device, then activate
a DRAM bank in place of the UCS memory block.
TMRIN1/PIO0
Timer Input 1 (input, synchronous, edge-sensitive)
This pin supplies a clock or control signal to the internal
microcontroller timer 1. After internally synchronizing a
Low-to-High transition on TMRIN1, the microcontroller
increments the timer. TMRIN1 must be tied High if not
being used. When PIO0 is enabled, TMRIN1 is pulled
High internally.
ONCE1—During reset, this pin and LCS/ONCE0 indi-
cate to the microcontroller the mode in which it should
operate. ONCE0 and ONCE1 are sampled on the ris-
ing edge of RES. If both pins are asserted Low, the mi-
crocontroller enters ONCE mode. Otherwise, it
operates normally. In ONCE mode, all pins assume a
high-impedance state and remain in that state until a
subsequent reset occurs. To guarantee that the micro-
controller does not inadvertently enter ONCE mode,
ONCE1 has a weak internal pullup resistor that is ac-
tive only during a reset.
TMRIN1 is driven internally by INT2/INTA0/PWD when
pulse width demodulation mode is enabled. The
TMRIN1/PIO0 pin can be used as a PIO when pulse
width demodulation mode is enabled.
TMROUT0/PIO10
Timer Output 0 (output, synchronous)
This pin supplies the system with either a single pulse
or a continuous waveform with a programmable duty
cycle. TMROUT0 is floated during a bus hold or reset.
UZI/PIO26
Upper Zero Indicate (output, synchronous)
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). UZI
is the logical AND of the inverted A19–A16 bits. It asserts
in the first period of a bus cycle and is held throughout the
cycle.
TMROUT1/PIO1
Timer Output 1 (output, synchronous)
This pin supplies the system with either a single pulse
or a continuous waveform with a programmable duty
cycle. TMROUT1 floats during a bus hold or reset.
V
TXD0/PIO22
CC
Power Supply (input)
Transmit Data 0 (output, asynchronous)
These pins supply power (+5 V) to the microcontroller.
This pin supplies asynchronous serial transmit data to
the system from serial port 0.
WHB
TXD1/PIO27
Write High Byte (output, three-state, synchronous)
Transmit Data 1 (output, asynchronous)
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, 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.
This pin supplies asynchronous serial transmit data to
the system from serial port 1.
Am186ED/EDLV Microcontrollers
31
AMD [ AMD ]
