Epson S1C33210 328

III PERIPHERAL BLOCK: SERIAL INTERFACE

Asynchronous Interface

Outline of Asynchronous Interface

Asynchronous transfers are performed by adding a start bit and a stop bit to the start and end points of each serial- converted data. With this method, there is no need to use a clock that is fully synchronized on the transmit and receive sides; instead, transfer operations are timed by the start and stop bits added to the start and end points of each data.

In the 8-bit asynchronous mode (SMDx[1:0] = "11"), 8 bits of data can be transferred; in the 7-bit asynchronous mode (SMDx[1:0] = "10"), 7 bits of data can be transferred.

In either mode, it is possible to select the stop-bit length, add a parity bit, and choose between even and odd parity. The start bit is fixed at "1".

The operating clock can be selected between an internal clock generated by an 8-bit programmable timer or an external clock that is input from the #SCLKx pin.

Since the transmit and receive units are both constructed with a double-buffer structure, successive transmit and receive operations are possible. Furthermore, since the transmit and receive units are independent, full-duplex communication in which transmit and receive operations are performed simultaneously is also possible.

Figure 8.8 shows an example of how input/output pins are connected for transfers in the asynchronous mode.

S1C33

External

S1C33

External

serial device

SINx

Data input

SINx

Data input

SOUTx

Data output

SOUTx

Data output

#SCLKx

External clock

(1) When external clock is used

(2) When internal clock is used

Figure 8.8 Example of Connection in Asynchronous Mode

When the asynchronous mode is selected, it is possible to use the IrDA interface function.

Asynchronous-transfer data format

The data format for asynchronous transfer is shown below.

Data length: 7 or 8 bits (determined by the selected transfer mode)

Start bit:

1 bit, fixed

Stop bit:

1 or 2 bits

Parity bit:

Even or odd parity, or none

Sampling clock (for transmitting)

7-bit asynchronous mode

(Stop bit: 1 bit, parity: none)

(Stop bit: 1 bit, parity: used)

(Stop bit: 2 bits, parity: none)

(Stop bit: 2 bits, parity: used)

8-bit asynchronous mode

(Stop bit: 1 bit, parity: none)

(Stop bit: 1 bit, parity: used)

(Stop bit: 2 bits, parity: non)

(Stop bit: 2 bits, parity: used)

s2 s3

s1: start bit, s2 & s3: stop bit, p: parity bit

Figure 8.9

Data Format for Asynchronous Transfer

Serial data is transmitted and received, starting with the LSB.

B-III-8-12

EPSON

S1C33210 FUNCTION PART