M37544 Datasheet, PDF (63/68 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

7544 Group
Notes on Serial I/O
1. Clock synchronous serial I/O
(1) When the transmit operation is stopped, clear the serial I/O en-
able bit (bit 7) and the transmit enable bit (bit 4 of serial I/O
control register (address 1A16)) to “0” (serial I/O and transmit
disabled).
<Reason>
Since transmission is not stopped and the transmission circuit is
not initialized even if only the serial I/O enable bit is cleared to “0”
(serial I/O disabled), the internal transmission is running (in this
case, since pins TxD, RxD, SCLK, and SRDY function as I/O ports,
the transmission data is not output). When data is written to the
transmit buffer register in this state, data starts to be shifted to the
transmit shift register. When the serial I/O enable bit is set to “1” at
this time, the data during internally shifting is output to the TxD pin
and an operation failure occurs.
(2) When the receive operation is stopped, clear the receive en-
able bit (bit 5) to “0” (receive disabled), or clear the serial I/O
enable bit (bit 7 of serial I/O control register (address 1A16)) to
“0” (serial I/O disabled).
(3) When the transmit/receive operation is stopped, clear both the
transmit enable bit and receive enable bit to “0” (transmit and
receive disabled) simultaneously. (any one of data transmis-
sion and reception cannot be stopped.)
<Reason>
In the clock synchronous serial I/O mode, the same clock is used
for transmission and reception.
If any one of transmission and reception is disabled, a bit error oc-
curs because transmission and reception cannot be synchronized.
In this mode, the clock circuit of the transmission circuit also oper-
ates for data reception. Accordingly, the transmission circuit does
not stop by clearing only the transmit enable bit to “0” (transmit
disabled). Also, the transmission circuit cannot be initialized even
if the serial I/O enable bit is cleared to “0” (serial I/O disabled)
(same as (1)).
(4) When signals are output from the SRDY pin on the reception
side by using an external clock, set all of the receive enable bit
(bit 5), the SRDY output enable bit (bit 2 of serial I/O control
register (address 1A16)), and the transmit enable bit to “1”.
(5) When the SRDY signal input is used, set the using pin to the in-
put mode before data is written to the transmit/receive buffer
register.
2. UART
When the transmit operation is stopped, clear the transmit enable
bit to “0” (transmit disabled).
<Reason>
Same as (1) shown on the above “1. Clock synchronous serial I/
O“.
When the receive operation is stopped, clear the receive enable
bit to “0” (receive disabled).
When the transmit/receive operation is stopped, clear the transmit
enable bit to “0” (transmit disabled) and receive enable bit to “0”
(receive disabled).
Rev.1.04 2004.06.08 page 63 of 66
REJ03B0012-0104Z
3. Notes common to clock synchronous serial I/O and UART
(1) Set the serial I/O control register again after the transmission
and the reception circuits are reset by clearing both the trans-
mit enable bit and the receive enable bit to “0.”
Clear both the transmit enable bit (TE)
and the receive enable bit (RE) to “0”
Set the bits 0 to 3 and bit 6 of the
serial I/O control register
Set both the transmit enable bit (TE)
and the receive enable bit (RE), or
one of them to “1”
Can be set
with the LDM
instruction at
the same time
Fig. 7 Sequence of setting serial I/O control register again
(2) The transmit shift completion flag (bit 2 of serial I/O status reg-
ister (address 1916)) changes from “1” to “0” with a delay of
0.5 to 1.5 shift clocks. When data transmission is controlled
with referring to the flag after writing the data to the transmit
buffer register, note the delay.
(3) When data transmission is executed at the state that an exter-
nal clock input is selected as the synchronous clock, set “1” to
the transmit enable bit while the SCLK is “H” state. Also, write
to the transmit buffer register while the SCLK is “H” state.
(4) When the transmit interrupt is used, set as the following se-
quence.
➀ Serial I/O transmit interrupt enable bit is set to “0” (disabled).
➁ Serial I/O transmit enable bit is set to “1”.
➂ Serial I/O transmit interrupt request bit (bit 1 of interrupt request
register 1 (address 3C16)) is set to “0” after 1 or more instruc-
tions have been executed.
➃ Serial I/O transmit interrupt enable bit (bit 1 of interrupt control
register 1 (address 3E16)) is set to “1” (enabled).
<Reason>
When the transmit enable bit is set to “1”, the transmit buffer
empty flag (bit 0) and transmit shift completion flag (bit 2 of serial
I/O status register (address 1916)) are set to “1”.
Accordingly, even if the timing when any of the above flags is set
to “1” is selected for the transmit interrupt source, interrupt request
occurs and the transmit interrupt request bit is set.
(5) Write to the baud rate generator (BRG) while the transmit/re-
ceive operation is stopped.