COP840C datasheet(14/35 Pages) NSC

14 / 35 page

Reset (Continued)

input (SI), serial data output (SO) and serial shift clock (SK).

Figure 6 shows the block diagram of the MICROWIRE/PLUS

interface.

The shift clock can be selected from either an internal source

or an external source. Operating the MICROWIRE/PLUS in-

terface with the internal clock source is called the Master

mode of operation. Operating the MICROWIRE/PLUS inter-

face with an external shift clock is called the Slave mode of

operation.

The CNTRL register is used to configure and control the

MICROWIRE/PLUS mode. To use the MICROWIRE/PLUS ,

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 register.

Table 4 details the different clock rates that

may be selected.

TABLE 4.

SL1

SL0

SK Cycle Time

where,

tc is the instruction cycle time.

MICROWIRE/PLUS OPERATION

Setting the BUSY bit in the PSW register causes the

MICROWIRE/PLUS arrangement 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 MICROWIRE/PLUS mode

either as a Master or as a Slave.

Figure 7 shows how two de-

vice microcontrollers and several peripherals may be inter-

connected using the MICROWIRE/PLUS arrangement.

MASTER MICROWIRE/PLUS OPERATION

In the MICROWIRE/PLUS Master mode of operation the

shift clock (SK) is generated internally by the device. The

MICROWIRE/PLUS Master always initiates all data ex-

changes (

Figure 7). The MSEL bit in the CNTRL register

must be set to enable the SO and SK functions on the G

Port. The SO and SK pins must also be selected as outputs

by setting appropriate bits in the Port G configuration regis-

ter.

Table 5 summarizes the bit settings required for Master

mode of operation.

SLAVE MICROWIRE/PLUS OPERATION

In the MICROWIRE/PLUS Slave mode of operation the SK

clock is generated by an external source. Setting the MSEL

bit in the CNTRL register enables the SO and SK functions

on the G Port. The SK pin must be selected as an input and

the SO pin selected as an output pin by appropriately setting

up the Port G configuration register.

Table 5 summarizes the

settings required to enter the Slave mode of operation.

DS011208-8

FIGURE 6. MICROWIRE/PLUS Block Diagram

DS011208-23

FIGURE 7. MICROWIRE/PLUS Application

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