COP888EB datasheet(46/75 Pages) NSC

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MICROWIRE/PLUS (Continued)

MICROWIRE/PLUS Master Mode Operation

In the MICROWIRE/PLUS Master mode of operation the

shift clock (SK) is generated internally. The MICROWIRE

Master always initiates all data exchanges. The MSEL bit in

the CNTRL register must be set to enable the SO and SK

functions onto the G Port. The SO and SK pins must also be

selected as outputs by setting appropriate bits in the Port G

configuraiton register.

Table 12 summarizes the bit settings

required for Master or Slave mode of operation.

TABLE 11. MICROWIRE/PLUS Master Mode

Clock Selection

SL1

SL0

2Xt

4Xt

8Xt

Where t

c is the instruction cycle clock

MICROWIRE/PLUS Slave Mode 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

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

and the SO pin is selected as an output pin by setting and re-

setting the appropriate bit in the Port G configuration regis-

ter.

Table 3 summarizes the settings required to enter the

Slave mode of operation.

The user must set the BUSY flag immediately upon entering

the Salve mode. This will ensure that all data bits sent by the

Master will be shifted properly. After eight clock pulses the

BUSY flag will be cleared and the sequence may be re-

peated.

Alternate SK Phase Operation

The device allows either the normal SK clock or an alternate

phase SK clock to shift data in and out of the SIO register. In

both the modes the SK is normally low. In the normal mode

data is shifted in on the rising edge of the SK clock and the

data is shifted out on the falling edge of the SK clock. The

SIO register is shifted on each falling edge of the SK clock in

the normal mode. In the alternate SK phase mode the SIO

A control flag, SKSEL, allows either the normal SK clock or

the alternate SK clock to be selected. Resetting SKSEL

causes the MICROWIRE/PLUS logic to be clocked from the

normal SK signal. Setting the SKSEL flag selects the alter-

nate SK clock. The SKSEL is mapped into the G6 configura-

tion bit. The SKSEL flag will power up in the reset condition,

selecting the normal SK signal.

TABLE 12. MICROWIRE/PLUS Mode Selection

This table assumes that the control flag MSEL is set.

Fun.

Operation

(SO)

(SK)

Config.

Bit

Int. SK

MICROWIRE/

PLUS Master

TRI-STATE

Int. SK

MICROWIRE/

PLUS Master

Ext. SK

MICROWIRE/

PLUS Slave

TRI-STATE

Ext. SK

MICROWIRE/

PLUS Slave

DS012837-37

FIGURE 35. MICROWIRE/PLUS Application

COP888EB Datasheet(PDF) 46 Page - National Semiconductor (TI)

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