19 UNIVERSAL SERIAL INTERFACE WITH LCD INTERFACE (USIL)
19-4
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
SPI master mode, LCD SPI mode
bps = f
SYS_CLK
×
DF / {(TR + 1)
×
2 + TFMD}
TR = (f
SYS_CLK
×
DF / bps - TFMD - 2) / 2
f
SOURCE
: T8 Ch.3 output clock frequency [Hz]
f
SYS_CLK
: System clock frequency [Hz]
bps:
Transfer rate [bps]
DF:
Division ratio set by DF[3:0]/T8_CLK3 register (T8 Ch.3)
TR:
Reload data to be set to the T8_TR3 register (T8 Ch.3)
TFMD: Fine mode set value at TFMD[3:0]/T8_CTL3 register (T8 Ch.3)
Example: UART mode, transfer rate = 115,200 bps, system clock = 33 MHz, DF[3:0]/T8_CLK3 register setting
(T8 Ch.3) = 1/1, TFMD[3:0]/T8_CTL3 register setting (T8 Ch.3) = 14
TR = (33,000,000
×
1 / 115,200 - 14 - 8) / 8 = 33.05 (= 0x21)
For more information on controlling the T8 module, refer to the “8-bit Timers (T8)” chapter.
Note: When the USIL is set to I
2
C slave mode, i2c_sck (I
2
C clock) is supplied from the external I
2
C
master. The T8 output clock frequency (f
SOURCE
) should be determined according to the i2c_sck
frequency.
T8 output clock
SCL controlled by I
2
C master
SCL controlled by I
2
C slave
USIL_CK pin
a b
c
d e f
3.1 I
Figure 19.
2
C Clock in I
2
C Slave Mode
Tbf = Ti2c_baud_rate
Tbc = Ti2c_baud_rate_high
Tcf = Ti2c_baud_rate_low
Tce: The I
2
C master occupies the SCL line by driving it to low.
Tac: The I
2
C master releases the SCL line.
Tdf: In order to finish the internal operations, the I
2
C slave occupies the SCL line for two
source clock (T8 output clock) cycles by driving it to low after detecting that the I
2
C mas-
ter drives the SCL line to low.
The T8 output clock frequency (f
SOURCE
) must be set so that the conditions shown below are satis-
fied.
f
SOURCE
> 3/Tbc
f
SOURCE
> 4/Tce
Be aware that the actual SCL signal will be delayed, as the I
2
C slave forcibly drives the SCL line
to low. The figure below shows an example in which the timing becomes worse.
T8 output clock
SCL controlled by I
2
C master
SCL controlled by I
2
C slave
USIL_CK pin
a b
c
d e
3.2 Example of Delayed I
Figure 19.
2
C Clock