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66 EPSON S1C88650 TECHNICAL MANUAL
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Serial Interface)
■ Data transmit procedure
The control procedure and operation during
transmitting is as follows.
(1) Write "0" in the transmit enable register TXEN
and the receive enable register RXEN to reset
the serial interface.
(2) Write "1" in the transmit enable register TXEN
to set into the transmitting enable status.
(3) Write the transmitting data into TRXD0–
TRXD7.
(4) In case of the master mode, confirm the receive
ready status on the slave side (external serial
input/output device), if necessary. Wait until it
reaches the receive ready status.
(5) Write "1" in the transmit control bit TXTRG and
start transmitting.
In the master mode, this control causes the
synchronous clock to change to enable and to be
provided to the shift register for transmitting
_________
and output from the SCLK terminal.
In the slave mode, it waits for the synchronous
_________
clock to be input from the SCLK terminal.
The transmitting data of the shift register shifts
one bit at a time at each falling edge of the
synchronous clock and is output from the SOUT
terminal. When the final bit (MSB when "LSB
first" is selected, or LSB when "MSB first" is
selected) is output, the SOUTx terminal is
maintained at that level, until the next
transmitting begins.
The transmitting complete interrupt factor flag
FSTRA is set to "1" at the point where the data
transmitting of the shift register is completed.
When interrupt has been enabled, a transmit-
ting complete interrupt is generated at this
point.
Set the following transmitting data using this
interrupt.
(6) Repeat steps (3) to (5) for the number of bytes of
transmitting data, and then set the transmit
disable status by writing "0" to the transmit
enable register TXEN, when the transmitting is
completed.
Data transmitting
End
TXEN ← 0, RXEN ← 0
No
Yes
Transmit complete ?
Set transmitting data
to TRXD0–TRXD7
No
Yes
FSTRA = 1 ?
TXEN ← 0
TXTRG ← 1
TXEN ← 1
No
Yes
Receiver ready ?
In case of master mode
Fig. 5.8.6.2 Transmit procedure in clock synchronous mode