S1C63558 TECHNICAL MANUAL
EPSON
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CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Serial Interface)
4.11.5 Transmit-receive control
Below is a description of the registers which handle transmit-receive control. With respect to transmit-
receive control procedures and operations, please refer to the following sections in which these are
discussed on a mode by mode basis.
Shift register and receive data buffer
Exclusive shift registers for transmitting and receiving are installed in this serial interface. Conse-
quently, duplex communication simultaneous transmit and receive is possible when the asynchronous
system is selected.
Data being transmitted are written to TRXD0–TRXD7 and converted to serial through the shift
register and is output from the SOUT terminal.
In the reception section, a receive data buffer is installed separate from the shift register.
Data being received are input to the SIN terminal and is converted to parallel through the shift
register and written to the receive data buffer.
Since the receive data buffer can be read even during serial input operation, the continuous data is
received efficiently.
However, since buffer functions are not used in clock synchronous mode, be sure to read out data
before the next data reception begins.
Transmit enable register and transmit control bit
For transmit control, use the transmit enable register TXEN and transmit control bit TXTRG.
The transmit enable register TXEN is used to set the transmit enable/disable status. When "1" is
written to this register to set the transmitting enable status, clock input to the shift register is enabled
and the system is ready to transmit data. In the clock synchronous mode, synchronous clock input/
output from the SCLK terminal is also enabled.
The transmit control bit TXTRG is used as the trigger to start transmitting data.
Data to be transmitted is written to the transmit data shift register, and when transmitting prepara-
tions a recomplete, "1" is written to TXTRG whereupon data transmitting begins.
When interrupt has been enabled, an interrupt is generated when the transmission is completed. If
there is subsequent data to be transmitted it can be sent using this interrupt.
In addition, TXTRG can be read as a status bit. When set to "1", it indicates transmitting operation,
and "0" indicates transmitting stop.
For details on timing, see the timing chart which gives the timing for each mode.
When not transmitting, set TXEN to "0" to disable transmition.
Receive enable register, receive control bit
For receiving control, use the receive enable register RXEN and receive control bit RXTRG.
Receive enable register RXEN is used to set receiving enable/disable status. When "1" is written into
this register to set the receiving enable status, clock input to the shift register is enabled and the
system is ready to receive data. In the clock synchronous mode, synchronous clock input/output from
the SCLK terminal is also enabled.
With the above setting, receiving begins and serial data input from the SIN terminal goes to the shift
register.
The operation of the receive control bit RXTRG is slightly different depending on whether a clock
synchronous system or an asynchronous system is being used.
In the clock synchronous system, the receive control bit TXTRG is used as the trigger to start receiving
data.
When received data has been read and the preparation for next data receiving is completed, write "1"
into RXTRG to start receiving. (When "1" is written to RXTRG in slave mode, SRDY switches to "0".)
