SRDY/PIO6
UCS/ONCE1
Synchronous Ready (input, synchronous,
level-sensitive)
Upper Memory Chip Select (output, synchronous)
ONCE Mode Request 1 (input, internal pullup)
This pin indicates to the microcontroller that the ad-
dressed memory space or I/O device will complete a
data transfer. The SRDY pin accepts an active High
input synchronized to CLKOUTA.
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 Kbyte. UCS is held High dur-
ing a bus hold condition.
Using SRDY instead of ARDY allows a relaxed system
timing because of the elimination of the one-half clock
period required to internally synchronize ARDY. To al-
ways assert the ready condition to the microcontroller,
tie SRDY High. If the system does not use SRDY, tie the
pin Low to yield control to ARDY. When SRDY is config-
ured as P106, the internal SRDY signal is driven low.
After power-on reset, UCS is asserted because the mi-
crocontroller begins executing at FFFF0h and the de-
fault configuration for the UCS chip select is 64 Kbyte
from F0000h to FFFFFh.
ONCE1—During reset, this pin and ONCE0 indicate to
the microcontroller the mode in which it should operate.
ONCE0 and ONCE1 are sampled on the rising edge of
RES. If both pins are asserted Low, the microcontroller
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 oc-
curs. To guarantee the microcontroller does not inad-
vertently enter ONCE mode, ONCE1 has a weak
internal pullup resistor that is active only during a reset.
TMRIN0/PIO11
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.
TMRIN1/PIO0
UZI/CLKSEL2/PIO26
Timer Input 1 (input, synchronous, edge-sensitive)
Upper Zero Indicate (output, synchronous)
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.
UZI—This pin lets the designer determine if an ac-
cess 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 Am186ER microcontroller and
AO15–AO10 on the Am188ER microcontroller). UZI
is the logical AND of the inverted A19–A16 bits. UZI
is not held throughout the cycle. UZI is asserted in
the first period and deasserted in the second period
of a bus cycle. UZI/CLKSEL2 is three-stated during
bus holds and ONCE mode.
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.
CLKSEL2—The clocking mode of the Am186ER and
Am188ER microcontrollers is controlled by UZI/
CLKSEL2/PIO26 and S6/CLKSEL1/PIO29 during re-
set. Both CLKSEL2 and CLKSEL1 are held High during
power-on reset because of an internal pullup resistor.
This is the default clocking mode—Times Four, which
is used if neither clock select is asserted Low during re-
set.
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.
TXD/PIO27
If CLKSEL2 is held Low during power-on reset, the mi-
crocontroller enters Times One mode.
Transmit Data (output, asynchronous)
This pin supplies asynchronous serial transmit data to
the system from the internal UART of the microcontrol-
ler.
This pin is latched within three crystal clock cycles after
the rising edge of RES. Refer to Reset Waveforms on
page 100 and Signals Related to Reset Waveforms on
page 100 to determine signal hold times. Note that
clock selection must be stable four clock cycles prior to
exiting reset (that is, RES going High). See Table 6 on
page 39 for specifics on the clocking modes and how to
specify them. UZI/CLKSEL2 is three-stated during bus
holds and ONCE mode.
38
Am186TMER and Am188TMER Microcontrollers Data Sheet
AMD [ AMD ]
