AMD Am186TMER, Am188TMER user manual Application Considerations, Clock Generation

1.3APPLICATION 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 1-3illustrates 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

10-MHz Crystal

Serial Port

RS-232

Level

Converter

	Am186ER		Am29F400
Microcontroller			Flash
X2		WR	WE
		A19–A0	Address
X1		AD15–AD0	Data
		RD	OE
		UCS	CS
	32 Kbyte
		RAM
		Timer 0–2
		INT4–INT0
TXD		DMA 0–1
			40 MHz
RXD		CLKOUTA

1.3.1Clock 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 1-3achieves 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.

1-6 Features and Performance