COP87L88KG Datasheet, PDF (29/42 Pages) National Semiconductor (TI) – 8-Bit One-Time Programmable (OTP) Microcontroller with UART and Three Multi-Function Timers

MICROWIRE PLUS (Continued)
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 If
enabled an interrupt is generated when eight data bits have
been shifted The device may enter the MICROWIRE PLUS
mode either as a Master or as a Slave Figure 18 shows
how two microcontroller devices and several peripherals
may be interconnected using the MICROWIRE PLUS ar-
rangements
Warning
The SIO register should only be loaded when the SK clock
is low Loading the SIO register while the SK clock is high
will result in undefined data in the SIO register SK clock is
normally low when not shifting
Setting the BUSY flag when the input SK clock is high in the
MICROWIRE PLUS slave mode may cause the current SK
clock for the SIO shift register to be narrow For safety the
BUSY flag should only be set when the input SK clock is
low
MICROWIRE PLUS Master Mode Operation
In the MICROWIRE PLUS Master mode of operation the
shift clock (SK) is generated internally by the device 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 configuration register Table IX
summarizes the bit settings required for Master mode of
operation
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 bits in the Port G configuration reg-
ister Table VI 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
repeated
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 shift-
ed in on the falling edge of the SK clock and shifted out on
the rising edge of the SK clock
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 IX
This table assumes that the control flag MSEL is set
G4 (SO) G5 (SK) G4 G5
Config Bit Config Bit Fun Fun
Operation
1
1
SO Int MICROWIRE PLUS
SK Master
0
1
TRI- Int MICROWIRE PLUS
STATE SK Master
1
0
SO Ext MICROWIRE PLUS
SK Slave
0
0
TRI- Ext MICROWIRE PLUS
STATE SK Slave
FIGURE 18 MICROWIRE PLUS Application
29
TL DD12864 – 20
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