
60
EPSON
S1C8F626 TECHNICAL MANUAL
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Serial Interface)
5.7.7 Operation of asynchronous transfer
Asynchronous transfer is a mode that transfers by
adding a start bit and a stop bit to the front and the
back of each piece of serial converted data. In this
mode, there is no need to use a clock that is fully
synchronized clock on the transmit side and the
receive side, but rather transmission is done while
adopting the synchronization at the start/stop bits
that have attached before and after each piece of
data. The RS-232C interface functions can be easily
realized by selecting this transfer mode.
This interface has separate transmit and receive
shift registers and is designed to permit full duplex
transmission to be done simultaneously for trans-
mitting and receiving.
The asynchronous mode supports a maximum
19200 bps of transfer rate in normal operating mode
or a maximum 600 bps in low power operating
mode.
For transfer data in the asynchronous 7-bit mode,
either 7 bits data (no parity) or 7 bits data + parity
bit can be selected. In the asynchronous 8-bit mode,
either 8 bits data (no parity) or 8 bits data + parity
bit can be selected.
Parity can be even or odd, and parity checking of
received data and adding a party bit to transmitting
data will be done automatically. Thereafter, it is not
necessary to be conscious of parity itself in the
program.
The start bit length is fixed at 1 bit. For the stop bit
length, either 1 bit or 2 bits can be selected using
the stop bit select register STPBx. Whether data is
transmitted/received from LSB (bit 0) or MSB (bit
7) it can be switched using the data input/output
permutation select register SDPx.
Sampling
clock
8bit data
D7 D6 D5 D4 D3 D2 D1 D0
s1
s2
7bit data
+parity
D6 D5 D4 D3 D2 D1 D0
p
s1
s2
8bit data
+parity
D7 D6 D5 D4 D3 D2 D1 D0
s1
p
s2
s1
s2
p
: Start bit (Low level, 1 bit)
: Stop bit (High level, 1 bit or 2 bits)
: Parity bit
7bit data
D6 D5 D4 D3 D2 D1 D0
s1
s2
Sampling
clock
LSB first
MSB first
8bit data
D0 D1 D2 D3 D4 D5 D6 D7
s1
s2
7bit data
+parity
D0 D1 D2 D3 D4 D5 D6
p
s1
s2
8bit data
+parity
D0 D1 D2 D3 D4 D5 D6 D7
s1
p
s2
7bit data
D0 D1 D2 D3 D4 D5 D6
s1
s2
Fig. 5.7.7.1 Transfer data configuration
for asynchronous system
Here following, we will explain the control se-
quence and operation for initialization and trans-
mitting /receiving in case of asynchronous data
transfer. See "5.7.9 Interrupt function" for the serial
interface interrupts.
■ Initialization of serial interface
The below initialization must be done in cases of
asynchronous system transfer.
(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.
(2) Port selection
Because serial interface input/output terminals
SINx and SOUTx are set as I/O port terminals
P10/P20 and P11/P21 at initial reset, "1" must
be written to the serial interface enable register
ESIFx in order to set these terminals for serial
interface use.
_________
SCLKx and SRDYx terminals set in the clock
synchronous mode are not used in the asyn-
chronous mode. These terminals function as I/
O port terminals P12/P22 and P13/P23.
(3) Setting of transfer mode
Select the asynchronous mode by writing the
data as indicated below to the two bits of the
mode selection registers SMDx0 and SMDx1.
7-bit mode:
SMDx0 = "0", SMDx1 = "1"
8-bit mode:
SMDx0 = "1", SMDx1 = "1"
(4) Parity bit selection
When checking and adding parity bits, write "1"
into the parity enable register EPRx to set to
"with parity check". As a result of this setting, in
the asynchronous 7-bit mode, it has a 7 bits data
+ parity bit configuration and in the asynchro-
nous 8-bit mode it has an 8 bits data + parity bit
configuration. In this case, parity checking for
receiving and adding a party bit for transmitting
is done automatically in hardware. Moreover,
when "with parity check" has been selected,
"odd" or "even" parity must be further selected in
the parity mode selection register PMDx.
When "0" is written to the EPRx register to select
"without parity check" in the asynchronous 7-bit
mode, data configuration is set to 7 bits data (no
parity) and in the asynchronous 8-bit mode (no
parity) it is set to 8 bits data (no parity) and parity
checking and parity bit adding will not be done.