COPC912C Datasheet, PDF (7/24 Pages) National Semiconductor (TI) – COP912C/COP912CH 8-Bit Microcontroller

Functional Description (Continued)
MICROWIRE PLUS
MICROWIRE PLUS is a serial synchronous communica-
tions interface The MICROWIRE PLUS capability enables
the device to interface with any of National Semiconductor’s
MICROWIRE peripherals (i e A D 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 or from an 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
SK
0
0
2 x tc
0
1
4 x tc
1
x
8 x tc
Where tc is the instruction cycle clock
MICROWIRE PLUS OPERATION
Setting the BUSY bit in the PSW register causes the MI-
CROWIRE PLUS 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 5 shows how two micro-
controllers and several peripherals may be interconnected
using the MICROWIRE PLUS arrangement
FIGURE 5 MICROWIRE PLUS Application
TL DD 12060 – 7
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