HD64F2145 Datasheet, PDF (515/829 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

17.4.3 Receive Abort
This LSI (system side) can forcibly abort transmission from the device connected to it (keyboard
side) in the event of a protocol error, etc. In this case, the system holds the clock low. During
reception, the keyboard also outputs a clock for synchronization, and the clock is monitored when
the keyboard output clock is high. If the clock is low at this time, the keyboard judges that there is
an abort request from the system, and data transmission from the keyboard is aborted. Thus the
system can abort reception by holding the clock low for a certain period. A sample receive abort
processing flowchart is shown in figure 17.7, and the receive abort timing in figure 17.8.
Start
[1] Read KBCRL, and if KBF = 1,
perform processing 1.
Receive state
Read KBCRL
KBF = 0?
No
Yes
Read KBCRH
RXCR3 to RXCR0 ≥
B'1001?
Yes
Disable receive abort
requests
No
[3]
[1]
Processing 1
[2] Read KBCRH, and if the value of
bits RXCR3 to RXCR0 is less than
B'1001, write 0 in KCLKO to abort
reception.
If the value of bits RXCR3 to
RXCR0 is B'1001 or greater, wait
until stop bit reception is
completed, then perform receive
data processing, and proceed to
the next operation.
KCLKO = 0
(receive abort request)
Retransmit
command transmission
(data)?
[3] If the value of bits RXCR3 to
RXCR0 is B'1001 or greater, the
parity bit is being received. With
the PS2 interface, a receive abort
[2]
request following parity bit
reception is disabled. Wait until
stop bit reception is completed,
perform receive data processing
and clear the KBF flag, then
proceed to the next operation.
No
Yes
KBE = 0
(disable KBBR reception
and clear receive counter)
KBE = 0
(disable KBBR reception
and clear receive counter)
Set start bit
(KDO = 0)
KBE = 1
(enable KB operation)
Clear I/O inhibit
(KCLKO = 1)
Clear I/O inhibit
(KCLKO = 1)
Transmit data
To transmit operation
To receive operation
Figure 17.7 (1) Sample Receive Abort Processing Flowchart
Rev. 2.0, 08/02, page 475 of 788