Operation Of Clock Synchronous Transfer - Epson S1C88655 Technical Manual

11.6 Operation of Clock
Synchronous Transfer
Clock synchronous transfer involves the transfer of
8-bit data by synchronizing it to eight clocks. The
same synchronous clock is used by both the
transmitting and receiving sides.
When the serial interface is used in the master
mode, the clock signal selected using SCSx0 and
SCSx1 is further divided by 1/16 and employed as
the synchronous clock. This signal is then sent via
___________
the SCLKx terminal to the slave side (external serial
I/O device).
When used in the slave mode, the clock input to the
___________
SCLKx terminal from the master side (external
serial input/output device) is used as the
synchronous clock.
In the clock synchronous mode, since one clock line
___________
(SCLKx) is shared for both transmitting and
receiving, transmitting and receiving cannot be
performed simultaneously. (Half duplex only is
possible in clock synchronous mode.)
The transfer data length is fixed at 8 bits. Data can
be switched using a register whether it is
transmitted/received from LSB (bit 0) or MSB (bit
7).
LSB first
SCLKx
LSB
Data D0 D1 D2 D3 D4 D5 D6 D7
MSB first
SCLKx
MSB
Data D7 D6 D5 D4 D3 D2 D1 D0
Fig. 11.6.1 Transfer data configuration using
clock synchronous mode
Below is a description of initialization when
performing clock synchronous transfer, transmit-
receive control procedures and operations.
With respect to serial interface interrupt, see "11.8
Interrupt Function".
Initialization of serial interface
When performing clock synchronous transfer,
the following initial settings must be made.
(1) Setting of transmitting/receiving disable
To set the serial interface into a status in which
both transmitting and receiving are disabled, "0"
must be written to both the transmit enable
register TXENx and the receive enable register
RXENx. Fix these two registers to a disable
status until data transfer actually begins.
S1C88655 TECHNICAL MANUAL
(2) Port selection
Because serial interface input/output ports
SINx, SOUTx, SCLKx and SRDYx are set as I/O
port terminals P10–P13 (P14–P17) at initial reset,
"1" must be written to the serial interface enable
register ESIFx in order to set these terminals for
serial interface use.
(3) Setting of transfer mode
Select the clock synchronous mode by writing
the data as indicated below to the two bits of the
mode selection registers SMDx0 and SMDx1.
Master mode:
Slave mode:
(4) Clock source selection
In the master mode, select the synchronous
clock source by writing data to the two bits of
the clock source selection registers SCSx0 and
SCSx1. (See Table 11.4.1.)
This selection is not necessary in the slave
mode.
Since all the registers mentioned in (2)–(4) are
assigned to the same address, it's possible to set
them all with one instruction. The parity enable
register EPRx is also assigned to this address,
however, since parity is not necessary in the
clock synchronous mode, parity check will not
take place regardless of how they are set.
(5) Clock source control
When the master mode is selected and pro-
MSB
grammable timer for the clock source is se-
lected, set transfer rate on the programmable
timer side. (See Chapter 13, "Programmable
Timer".)
When the divided signal of OSC3 oscillation
circuit is selected for the clock source, be sure
LSB
that the OSC3 oscillation circuit is turned ON
prior to commencing data transfer. (See Chapter
8, "Oscillation Circuits".)
(6) Serial data input/output permutation
The S1C88655 provides the data input/output
permutation select register SDPx to select
whether the serial data bits are transferred from
the LSB or MSB. The SDPx register should be set
before writing data to TXDx0–TXDx7.
EPSON
11 SERIAL INTERFACE
___________ ___________
SMDx0 = "0", SMDx1 = "0"
SMDx0 = "1", SMDx1 = "0"
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