COPC912C datasheet(7/24 Pages) NSC

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Functional Description (Continued)

MICROWIREPLUS

MICROWIREPLUS is a serial synchronous communica-

tions interface The MICROWIREPLUS capability enables

the device to interface with any of National Semiconductor’s

MICROWIRE peripherals (ie AD converters display driv-

ers EEPROMS etc) and with other microcontrollers which

support the MICROWIRE interface It consists of an 8-bit

serial shift register (SIO) with serial data input (SI) serial

data output (SO) and serial shift clock (SK)

Figure 5 shows

a block diagram of the MICROWIRE logic

The shift clock can be derived from either the internal

source

from

external

source

Operating

the

MICROWIRE arrangement with the internal clock source is

called the Master mode of operation Similarly operating

the MICROWIRE arrangement with an external shift clock is

called the Slave mode of operation

The CNTRL register is used to configure and control the

MICROWIRE mode To use the MICROWIRE the MSEL bit

in the CNTRL register is set to one The SK clock rate is

selected by the two bits SL0 and SL1 in the CNTRL regis-

ter

The following table details the different clock rates that may

be selected

SK Divide Clock Rates

SL1

SL0

2xtc

4xtc

8xtc

Where tc is the instruction cycle clock

MICROWIREPLUS OPERATION

Setting the BUSY bit in the PSW register causes the MI-

CROWIREPLUS to start shifting the data It gets reset

when eight data bits have been shifted The user may reset

the BUSY bit by software to allow less than 8 bits to shift

The device may enter the MICROWIREPLUS mode either

as a Master or as a Slave

Figure 5 shows how two micro-

controllers and several peripherals may be interconnected

using the MICROWIREPLUS arrangement

TLDD12060 – 7

FIGURE 5 MICROWIREPLUS Application

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