13 SeRial inTeRFaCe
13-4
Seiko epson Corporation
S1C63003/004/008/016 TeChniCal Manual
(Rev. 1.1)
Setting Synchronous Clock
13.5
Selecting Source Clock
13.5.1
When the serial interface is used in master mode, it uses the internal clock supplied from the clock manager as the
synchronous clock for data transfer. The clock manager generates six serial interface clocks by dividing the OSC1
or OSC3 clock. The synchronous clock used in master mode can be selected from seven types (the above six clocks
and the programmable timer 1 output clock). Use the SIFCKS[2:0] register to select one of them as shown in Table
13.5.1.1.
5.1.1 Serial interface clock frequencies
Table 13.
SIFCKS[2:0]
SIF clock (master mode)
7
f
OSC3
/ 4
*
6
f
OSC3
/ 2
*
5
f
OSC3
/ 1
*
4
Programmable timer 1
*
3
f
OSC1
/ 4 (8 kHz)
2
f
OSC1
/ 2 (16 kHz)
1
f
OSC1
/ 1 (32 kHz)
0
Off (slave mode)
*
f
OSC1
: OSC1 oscillation frequency. ( ) indicates the frequency when f
OSC1
= 32 kHz.
f
OSC3
: OSC3 oscillation frequency
*
The maximum clock frequency is limited to 1 MHz.
When programmable timer 1 is selected, the programmable timer 1 underflow signal is divided by 2 before it is used
as the synchronous clock. In this case, the programmable timer must be controlled before operating the serial inter-
face. Refer to the "Programmable Timer" chapter for controlling the programmable timer.
Fix SIFCKS[2:0] at "0" in slave mode.
At initial reset, "Off (slave mode)" is selected.
Selecting Synchronous Clock Format
13.5.2
The format (polarity and phase) of the synchronous clock for the serial interface can be configured using the
SCPS[1:0] register.
5.2.1 Configuration of synchronous clock format
Table 13.
SCPS[1:0]
Polarity
Phase
3
Negative (SCLK)
Rising edge (
↑
)
2
Negative (SCLK)
Falling edge (
↓
)
1
Positive (SCLK)
Falling edge (
↓
)
0
Positive (SCLK)
Rising edge (
↑
)
At initial reset, the clock polarity is set to positive and the phase is set to the rising edge.
See Figure 13.6.5.1 for the data transfer timings by the synchronous clock format selected.