COP888CL Datasheet, PDF (27/42 Pages) Texas Instruments – COP888CL 8-Bit Microcontroller

MICROWIRE/PLUS (Continued)
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
resetting the appropriate bit in the Port G configuration reg-
ister. Table V summarizes the settings required to enter the
Slave mode of operation.
The user must set the BUSY flag immediately upon entering
the Slave 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 alternate SK phase operation, data is shifted in on the
falling edge of the SK clock and shifted out on the rising edge
of the SK clock.
FIGURE 14. MICROWIRE/PLUS Application
DS009766-21
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 configu-
ration bit. The SKSEL flag will power up in the reset condi-
tion, selecting the normal SK signal.
This table assumes that the control flag MSEL is set.
G4
(SO)
Config.
Bit
1
0
1
0
TABLE 7.
G5
(SK)
Config.
Bit
1
G4
Fun.
SO
1
TRI-
STATE
0
SO
0
TRI-
STATE
G5
Fun.
Int.
SK
Int.
SK
Ext.
SK
Ext.
SK
Operation
MICROWIRE/PLUS
Master
MICROWIRE/PLUS
Master
MICROWIRE/PLUS
Slave
MICROWIRE/PLUS
Slave
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