PSEN1
Mux
Power-Save
Divisor1
(/1 to /128)
CPU Clock
CAF1
CLKSEL2
CAD1
Mux
PLL
1x or 4x
CLKOUTA
CLKOUTB
Mux
Fundamental
Clock
X1, X2
Input Clock
CBF1
CBD1
÷2
Time
Delay
Mux
CLKSEL1
6 ±2.5ns
Notes:
1. Set via PDCON Register
Figure 10. Clock Organization
as RES is active. After RES becomes inactive and an
internal processing interval elapses, the microcontrol-
ler begins execution with the instruction at physical lo-
cation FFFF0h. RES also sets some registers to
predefined values. Note that all clock selection (S6/
CLKSEL1 and UZI/CLKSEL2) must be stable four
clocks prior to the deassertion of RES. Activating the
PLL will require 1 ms to achieve a stable clock.
System Clocks
The base system clock of the original Am186/Am188
microcontrollers is renamed CLKOUTA and the addi-
tional output is called CLKOUTB. CLKOUTA and CLK-
OUTB operate at either the fundamental processor
frequency or the CPU clock (power-save) frequency.
Figure 10 shows the organization of the clocks.
The second clock output (CLKOUTB) allows one clock
to run at the fundamental frequency and the other clock
to run at the CPU (power-save) frequency. Individual
drive enable bits allow selective enabling of just one, or
both, of these clock outputs.
Reset Configuration Register
When the RES input is asserted Low, the contents of
the address/data bus (AD15–AD0) are written into the
Reset Configuration Register. The system can place
configuration information on the address/data bus
using weak external pullup or pulldown resistors, or
using an external driver that is enabled during reset.
The processor does not drive the address/data bus
during reset.
Power-Save Operation
The Power-Save mode of the Am186ER and
Am188ER microcontrollers reduces power consump-
tion and heat dissipation, thereby extending battery life
in portable systems. In Power-Save mode, operation of
the CPU and internal peripherals continues at a slower
clock frequency. When a hardware interrupt occurs, the
microcontroller automatically returns to its normal op-
erating frequency. The microcontroller remains in
Power-Save mode for software interrupts and traps.
For example, the Reset Configuration Register could
be used to provide the software with the position of a
configuration switch in the system. Using weak external
pullup and pulldown resistors on the address and data
bus, the system would provide the microcontroller with
a value corresponding to the position of the jumper dur-
ing a reset.
Note: Power-save operation requires that clock-
dependent peripherals be reprogrammed for clock
frequency changes. Software drivers must be aware of
clock frequency.
The Reset Configuration Register can only be modified
during reset. This register is read-only during normal
operation.
Initialization and Processor Reset
Processor initialization or startup is accomplished by
driving the RES input pin Low. RES must be held Low
for 1 ms during power-up to ensure proper device ini-
tialization. RES forces the Am186ER and Am188ER
microcontrollers to terminate all execution and local
bus activity. No instruction or bus activity occurs as long
48
Am186TMER and Am188TMER Microcontrollers Data Sheet
AMD [ AMD ]
