SD188ES/SD188EM Demonstration Board User’s Manual
2-10
1.1
Clock and Reset Logic
The Am188ES and Am188EM microcontrollers can be configured for either 1x
or ½x clock mode. As configured on the SD188ES/SD188EM demonstration
board, the microcontroller is in 1x clock mode. The input is generated by a 40-
MHz fundamental mode crystal (Y1) that is connected to the X1/X2 inputs of the
microcontrollers, resulting in a 40-MHz system clock.
System reset is controlled by a voltage supply supervisor (TI TL7705A, U1). This
device generates the processor’s reset input, asserting the Am188ES or Am188EM
microcontroller’s RES pin for 13 ms when the RESET switch is depressed. The voltage
supply supervisor also holds reset active when the power falls below 4.75 V.
Am188 Expansion Interface
The SD188ES/SD188EM demonstration board supports the PC/104 form-factor
expansion-type connector for additional prototyping and testing. The traditional
PC/104 signals are not present on the board; however, the Am188 expansion
interface enables you to attach wirewrap or prototype boards that have the same
standard physical interface. The pinout of the expansion interface for the SD188ES
is shown in the figures that follow.
NOTE:
The pinout of the expansion interface is identical for both the SD188ES
and SD188EM demonstration boards except for the four pins shown in Table 2-2.
Table 2-2. Expansion Interface SD188ES/SD188EM Pinout
Differences
J2 Pin
Number
SD188ES
Pin Name
SD188EM
Pin Name
B19
RTS0
SCLK
B20
TXD0
SDEN0
B21
RXD0
SDEN1
B22
CTS0
SDATA
frtbook : newch2 Page 10 Monday, June 2, 1997 3:37 PM