III PERIPHERAL BLOCK: SERIAL INTERFACE

Setting Asynchronous Interface

When performing asynchronous transfer via the serial interface, the following must be done before data transfer can be started:

1.Setting input/output pins

2.Setting the interface mode

3.Setting the transfer mode

4.Setting the input clock

5.Setting the data format

6.Setting interrupt/IDMA/HSDMA

The following describes how to set each of the above. For details on interrupt/DMA settings, refer to "Serial Interface Interrupts and DMA".

Note: Always make sure the serial interface is inactive (TXENx and RXENx = "0") before making these settings. A change in settings during operation may result in a malfunction.

Setting input/output pins

In the asynchronous mode, two pins–SINx and SOUTx–are used. When external clock input is used for Ch. 0 and Ch. 2, one more pin, #SCLKx, is also used.

Set CFP0[7:0] (D[7:0]) / P0 function select register (0x402D0) according to the pins used. (Both channels can be used, if necessary.) Since the #SRDYx pin is not used, P03 or P24 can be used as an I/O port. During operation using the internal clock, P02 or P25 can also be used as an I/O port.

Setting the interface mode

IRMDx[1:0] (D[1:0]) / Serial I/F IrDA register (Ch.0: 0x401E4, Ch.1: 0x401E9, Ch.2: 0x401F4, Ch.3: 0x401F9) is used to set the IrDA interface. Since IRMDx[1:0] becomes indeterminate at initial reset, initialize it by writing "00" when using the serial interface as a normal interface, or "10" when using the serial interface as an IrDA interface. This setting must be made before a transfer mode is set.

Setting the transfer mode

Use SMDx to set the transfer mode of the serial interface as described earlier.When using the serial interface in the 8-bit asynchronous mode, set SMDx[1:0] to "11", when using the serial interface in the 7-bit asynchronous mode, set SMDx[1:0] to "10".

Setting the input clock

In the asynchronous mode, the operating clock can be selected between the internal clock and an external clock. Ch.0 input clock selection: SSCK0 (D2) / Serial I/F Ch.0 control register (0x401E3)

Ch.1 input clock selection: SSCK1 (D2) / Serial I/F Ch.1 control register (0x401E8)

Ch.2 input clock selection: SSCK2 (D2) / Serial I/F Ch.2 control register (0x401F3)

Ch.3 input clock selection: SSCK3 (D2) / Serial I/F Ch.3 control register (0x401F8)

The external clock is selected (input from the #SCLKx pin) by writing "1" to SSCKx, and an internal clock is selected by writing "0".

Note: SSCKx becomes indeterminate at initial reset, so be sure to reset it in the software.

SSCK11 and SSCK31 must be "0" because Ch. 1 and Ch. 3 support only asynchronous operation.

•Internal clock

When the internal clock is selected, the serial interface is clocked by a clock generated using an 8-bit programmable timer. The clock source for each channel is as follows:

Ch.0: Clock output by 8-bit programmable timer 2

Ch.1: Clock output by 8-bit programmable timer 3

Ch.2: Clock output by 8-bit programmable timer 4

Ch.3: Clock output by 8-bit programmable timer 5

Therefore, before the internal clock can be used, the following conditions must be met:

1.The prescaler is outputting a clock to the 8-bit programmable timer 2 (or 3).

2.The 8-bit programmable timer 2 (or 3) is outputting a clock.

S1C33210 FUNCTION PART

EPSON

B-III-8-13