MC68HC11A1MFN2 Просмотр технического описания (PDF) - Motorola => Freescale

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MC68HC11A1MFN2

HCMOS Single-Chip Microcontroller

Motorola => Freescale 

2.1.8 A/D Converter Reference Voltages (VRL, VRH)

These two inputs provide the reference voltages for the analog-to-digital converter cir-

cuitry.

2

2.1.9 Strobe B and Read/Write (STRB/R/W)

This signal acts as a strobe B output or as a data bus direction indicator depending on

the operating mode.

In single-chip operating mode, the STRB output acts as a programmable strobe for

handshake with other parallel l/O devices. Refer to 4 PARALLEL I/O for additional in-

formation.

In expanded multiplexed operating mode, R/W is used to control the direction of trans-

fers on the external data bus. A low on the R/W signal indicates data is being written

to the external data bus. A high on this signal indicates that a read cycle is in progress.

R/W will stay low during consecutive data bus write cycles, such as in a double-byte

store. The NAND of inverted R/W with the E clock should be used as the write enable

signal for an external static RAM.

2.1.10 Strobe A and Address Strobe (STRA/AS)

This signal acts as an edge detecting strobe A input or as an address strobe bus con-

trol output depending on the operating mode.

In single-chip operating mode, the STRA input acts as a programmable strobe for

handshake with other parallel l/O devices. Refer to 4 PARALLEL I/O for additional in-

formation.

In expanded multiplexed operating mode, the AS output is used to demultiplex the ad-

dress and data signals at port C. Refer to 2.2.2 Expanded Multiplexed Operating

Mode for additional information.

2.1.11 Port Signals

Ports A, D, and E signals are independent of the operating mode. Port B provides eight

general purpose output signals in single-chip operating modes and provides eight

high-order address signals when the microcontroller is in expanded multiplexed oper-

ating modes. Port C provides eight general purpose input/output signals when the mi-

crocontroller is in singlechip operating modes. When the microcontroller is in

expanded multiplexed operating modes, port C is used for a multiplexed address/data

bus. Table 2-2 shows a summary of the 40 port signals as they relate to the operating

modes. Unused inputs and l/O pins configured as inputs should be terminated high or

low.

MOTOROLA

2-4

SIGNAL DESCRIPTIONS AND OPERATING MODES

MC68HC11A8

TECHNICAL DATA

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