cop87l88fh National Semiconductor Corporation, cop87l88fh Datasheet - Page 32

• Manufacturer Part Number: cop87l88fh
• Description: 8-bit Cmos Otp Microcontrollers With 16k Memory, Comparators, Usart And Hardware Multiply/divide
• Manufacturer: National Semiconductor Corporation

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MICROWIRE/PLUS
MICROWIRE/PLUS OPERATION
Setting the BUSY bit in the PSW register causes the
MICROWIRE/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 20 shows how
two devices, microcontrollers and several peripherals may
be interconnected using the MICROWIRE/PLUS arrange-
ments.
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 nor-
mally 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 MI-
CROWIRE 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 VII 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
Where t
TABLE 10. MICROWIRE/PLUS
SL1
0
0
1
Master Mode Clock Select
c
is the instruction cycle clock
Don’t Care
Don’t Care
Mismatch
Match
Data
Key
SL0
0
1
x
(Continued)
Don’t Care
Don’t Care
2 x t
4 x t
8 x t
Mismatch
Window
Match
Data
c
c
c
SK
TABLE 9. WATCHDOG Service Actions
Don’t Care
Don’t Care
Mismatch
Monitor
Clock
Match
32
Valid Service: Restart Service Window
Error: Generate WATCHDOG Output
Error: Generate WATCHDOG Output
Error: Generate WATCHDOG Output
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 bits in the Port G configuration regis-
ter. Table VII 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.
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.
This table assumes that the control flag MSEL is set.
G4 (SO)
Config.
Bit
1
0
1
0
TABLE 11. MICROWIRE/PLUS Mode Settings
Config. Bit
G5 (SK)
Action
1
1
0
0
STATE
STATE
Fun.
TRI-
TRI-
G4
SO
SO
Fun.
Ext.
Ext.
G5
Int.
SK
Int.
SK
SK
SK
MICROWIRE/PLUS
Master
MICROWIRE/PLUS
Master
MICROWIRE/PLUS
Slave
MICROWIRE/PLUS
Slave
Operation