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Features and Performance
1-6
1.3 APPLICATION CONSIDERATIONS
The integration enhancements of the Am186ER and Am188ER microcontrollers provide a
high-performance, low-system-cost solution for 16-bit embedded microcontroller designs.
The internal 32-Kbyte RAM allows the manufacture of a complete embedded system using
only one external ROM device and a low-cost crystal, plus any voltage conversion or current
drivers required for I/O. Internal RAM is enabled and configured by using the Internal
Memory Chip Select (IMCS) Register described in Chapter 6, “Internal Memory.”
The nonmultiplexed address bus (A19–A0) eliminates system-interface logic for external
memory, while the multiplexed address/data bus maintains the value of existing customer-
specific peripherals and circuits within the upgraded design.
The nonmultiplexed address bus is available in addition to the 80C186 and 80C188
microcontrollers’ multiplexed address/data bus (AD15–AD0). The two buses can operate
simultaneously, or the AD15–AD0 bus can be configured to operate only during the data
phase of a bus cycle. See the BHE
/ADEN and RFSH2/ADEN pin descriptions in Chapter 3,
and see section 5.5.1 and section 5.5.2 for additional information regarding the AD15–AD0
address enabling and disabling.
Figure 1-3 illustrates a functional system design that uses the integrated peripheral set to
achieve high performance with reduced system cost.
Figure 1-3 Basic Functional System Design
1.3.1 Clock Generation
The integrated PLL clock-generation circuitry of the Am186ER and Am188ER
microcontrollers allows operation at one times or four times the crystal frequency, in addition
to the one-half frequency operation required by 80C186 and 80C188 microcontrollers. The
design in Figure 1-3 achieves 40-MHz CPU operation with a 10-MHz crystal.
The integrated PLL lowers system cost by reducing the cost of the crystal and reduces
electromagnetic interference (EMI) in the system.
X2
X1
RS-232
Level
Converter
TXD
RXD
UCS
WR
RD
WE
OE
CS
AD15–AD0
A19–A0
Serial Port
Am186ER
Microcontroller
10-MHz
Crystal
Address
Data
32 Kbyte
RAM
Timer 0–2
INT4–INT0
DMA 0–1
CLKOUTA
40 MHz
Am29F400
Flash