M16C30P_07 Datasheet, PDF (295/317 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/30 SERIES

M16C/30P Group
22. Usage Precaution
22.9 Precautions for Serial interface
22.9.1 Clock Synchronous Serial I/O
22.9.1.1 Transmission/reception
With an external clock selected, and choosing the RTS function, the output level of the RTSi pin goes to “L” when
the data-receivable status becomes ready, which informs the transmission side that the reception has become ready.
The output level of the RTSi pin goes to “H” when reception starts. So if the RTSi pin is connected to the CTSi pin
on the transmission side, the circuit can transmission and reception data with consistent timing. With the internal
clock, the RTS function has no effect.
22.9.1.2 Transmission
When an external clock is selected, the conditions must be met while if the CKPOL bit in the UiC0 register = 0
(transmit data output at the falling edge and the receive data taken in at the rising edge of the transfer clock), the
external clock is in the high state; if the CKPOL bit in the UiC0 register = 1 (transmit data output at the rising
edge and the receive data taken in at the falling edge of the transfer clock), the external clock is in the low state.
• The TE bit in the UiC1 register= 1 (transmission enabled)
• The TI bit in the UiC1 register = 0 (data present in UiTB register)
• If CTS function is selected, input on the CTSi pin = L
22.9.1.3 Reception
In operating the clock-synchronous serial I/O, operating a transmitter generates a shift clock. Fix settings for
transmission even when using the device only for reception. Dummy data is output to the outside from the
TXDi pin when receiving data.
When an internal clock is selected, set the TE bit in the UiC1 register (i = 0 to 2) to 1 (transmission enabled) and
write dummy data to the UiTB register, and the shift clock will thereby be generated.
When an external clock is selected, set the TE bit to 1 and write dummy data to the UiTB register, and the shift
clock will be generated when the external clock is fed to the CLKi input pin.
When successively receiving data, if all bits of the next receive data are prepared in the UARTi receive register
while the RE bit in the UiC1 register (i = 0 to 2) = 1 (data present in the UiRB register), an overrun error occurs
and the OER bit in the UiRB register is set to “1” (overrun error occurred). In this case, because the content of
the UiRB register is indeterminate, a corrective measure must be taken by programs on the transmit and receive
sides so that the valid data before the overrun error occurred will be retransmitted. Note that when an overrun
error occurred, the IR bit in the SiRIC register does not change state.
To receive data in succession, set dummy data in the lower-order byte of the UiTB register every time reception
is made.
When an external clock is selected, the conditions must be met while if the CKPOL bit = 0, the external clock is
in the high state; if the CKPOL bit = 1, the external clock is in the low state.
• The RE bit in the UiC1 register= 1 (reception enabled)
• The TE bit in the UiC1 register= 1 (transmission enabled)
• The TI bit in the UiC1 register= 0 (data present in the UiTB register)
Rev.1.22 Mar 29, 2007 Page 279 of 291
REJ09B0179-0122