AMD Am186 CC User Manual page 65

Table 3-7 Signal Descriptions (Continued)
Multiplexed
1
Signal Name
Signal(s)
RES
RESOUT
[USBSOF]
[UCLK] [USBSCI]
PIO21
USBX1 CC CU
USBX2 CC CU
X1
X2
System Overview
Type Description
Reset requires the microcontroller to perform a reset. When RES
is asserted, the microcontroller immediately terminates its
present activity, clears its internal logic, and on the deassertion
of RES, transfers CPU control to the reset address FFFF0h.
RES must be asserted for at least 1 ms to allow the internal
circuits to stabilize.
RES can be asserted asynchronously to CLKOUT because RES
is synchronized internally. For proper initialization, V
within specifications, and CLKOUT must be stable for more than
four CLKOUT periods during which RES is asserted.
— STI
If RES is asserted while the watchdog timer is performing a
watchdog-timer reset, the external reset takes precedence over
the watchdog-timer reset. This means that the RESOUT signal
asserts as with any external reset and the WDTCON register
will not have the RSTFLAG bit set. In addition, the microcontroller
will exit reset based on the external reset timing, i.e., 4.5 clocks
after the deassertion of RES rather than 2
watchdog timer timeout occurred.
The microcontroller begins fetching instructions approximately
6.5 CLKOUT periods after RES is deasserted. This input is
provided with a Schmitt trigger to facilitate power-on RES
generation via a resistor-capacitor (RC) network.
Reset Out indicates that the microcontroller is being reset (either
externally or internally), and the signal can be used as a system
reset to reset any external peripherals connected to RESOUT.
— O
During an external reset, RESOUT remains active (High) for two
clocks after RES is deasserted. The microcontroller exits reset
and begins the first valid bus cycle approximately 4.5 clocks after
RES is deasserted.
UART Clock can be used instead of the processor clock as the
source clock for either the UART or the High-Speed UART. The
STI
source clock for the UART and the High-Speed UART are
selected independently and both can use the same source.
USB Controller Crystal Input (USBX1) and USB Controller
Crystal Output (USBX2) provide connections for a fundamental
— STI mode, parallel-resonant crystal used by the internal USB
oscillator circuit.
— O
If the CPU crystal is used to generate the USB clock, USBX1
must be pulled down.
CPU Crystal Input (X1) and CPU Crystal Output (X2) provide
— O
connections for a fundamental mode, parallel-resonant crystal
used by the internal oscillator circuit. If an external oscillator is
— STI
used, inject the signal directly into X1 and leave X2 floating.
Am186™CC/CH/CU Microcontrollers User's Manual
must be
CC
16
clocks after the
3-15