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CHAPTER 17 SERIAL INTERFACE CSI1
319
User’s Manual U14260EJ3V1UD
Figure 17-1. Block Diagram of Serial Interface CSI1
(1) Transmit buffer register 1 (SOTB1)
This register sets transmit data.
Transmission is started by writing data to SOTB1 when bit 7 (CSIE1) and bit 6 (TRMD1) of serial operation mode
register 1 (CSIM1) are 1.
The data written to SOTB1 is converted from parallel data into serial data by serial I/O shift register 1, and output
to the serial output (SO1) pin.
SOTB1 can be written or read by an 8-bit memory manipulation instruction.
RESET input makes SOTB1 undefined.
Cautions 1. Do not access SOTB1 when CSOT1 = 1 (during serial communication).
2. The SS1 pin can be used in the slave mode. For details of the transmission/reception
operation, see 17.4.2 (2) Communication operation.
(2) Serial I/O shift register 1 (SIO1)
This is an 8-bit register that converts data from parallel into serial or vice versa.
The reception status is entered by reading data from SIO1 if bit 7 (CSIE1) of serial operation mode register 1
(CSIM1) is 1.
During reception, data is read from the serial input pin (SI1) to SIO1.
SIO1 can be read by an 8-bit memory manipulation instruction.
RESET input makes SIO1 undefined.
Cautions 1. Do not access SIO1 when CSOT1 = 1 (during serial communication).
2. The SS1 pin can be used in the slave mode. For details of the transmission/reception
operation, see 17.4.2 (2) Communication operation.
17.3 Registers to Control Serial Interface CSI1
Serial interface CSI1 is controlled by the following four registers.
Serial operation mode register 1 (CSIM1)
Serial clock select register 1 (CSIC1)
Port mode register 2 (PM2)
Port register 2 (P2)
8
8
8
Output latch
(P21)
PM21
SS1
SO1/P21
INTCSI1
SI1/P20
f
X
/2
f
X
/2
2
f
X
/2
3
f
X
/2
4
f
X
/2
5
f
X
/2
6
f
X
/2
7
SCK1/P22
Output
selector
Internal bus
Serial I/O shift
register 1 (SIO1)
Transmit buffer
register 1 (SOTB1)
Output latch
Transmit controller
Clock start/stop controller &
clock phase controller
Transmit data
controller
S