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III PERIPHERAL BLOCK: SERIAL INTERFACE
S1C33210 FUNCTION PART EPSON B-III-8-5
Setting Clock-Synchronized Interface
When performing clock-synchronized transfers via the serial interface, the following settings must be made before
data transfer is actually begun:
1. Setting input/output pins
2. Setting the interface mode
3. Setting the transfer mode
4. Setting the input clock
5. Setting interrupts and IDMA/HSDMA
The following explains the content of each setting. 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 these settings
are made. A change of settings during operation may cause a malfunction.
Setting input/output pins
All four pins—SINx, SOUTx, #SCLKx, and #SRDYx—are used in the clock-synchronized mode. When using
Ch.0, set CFP0[3:0] (D[3:0]) / P0 function select register (0x402D0) to "1111" and when using Ch.2, set D[3:0]
/ Port SIO function extension register (0x402DB) to "1111". (It is possible to use both channels.)
Note: Ch. 1 and Ch. 3 support only asynchronous operation.
Setting the interface mode
IRMDx[1:0] (D[1:0]) / Serial I/F Ch.0 IrDA register (0x401E4) or Serial I/F Ch.2 IrDA register (0x401F4) is
used to set the interface mode (normal or IrDA interface). Write "00" to IRMDx[1:0] to choose the ordinary
interface. Since IRMDx[1:0] becomes indeterminate at initial reset, it must be initialized.
Setting the transfer mode
Use SMDx to set the transfer mode of the serial interface as described earlier. When using the serial interface as
the master for clock-synchronized transfer, set SMDx[1:0] to "00"; when using the serial interface as a slave, set
SMDx[1:0] to "01".
Setting the input clock
• Clock-synchronized master mode
This mode operates using an internally derived clock. The clock source for each channel is as follows:
Ch.0: A clock output by 8-bit programmable timer 2
Ch.1: A clock output by 8-bit programmable timer 3
Ch.2: A clock output by 8-bit programmable timer 4
Ch.3: A clock output by 8-bit programmable timer 5
Therefore, in order for the serial interface to be used in the clock-synchronized master mode, the following
conditions must be met:
1. The prescaler is feeding a clock to 8-bit programmable timer 2 (3).
2. The 8-bit programmable timer 2 (3) is generating a clock.
Any desired clock frequency can be selected by setting the division ratio of the prescaler and the reload data of
the 8-bit programmable timer as necessary. The relationship between the contents of these settings and the
transfer rate is expressed by Eq. 1 below.
To ensure that the duty ratio of the clock to be fed to the serial interface is 50%, the 8-bit programmable timer
further divides the underflow signal frequency by 2 internally. This 1/2 frequency division is factored into Eq.
1.