Renesas H8S/2318 series, Hardware Manual

Page: 464 / 1121

Rev. 5.00, 12/03, page 434 of 1088
Bits 1 and 0—Clock Enable 1 and 0 (CKE1, CKE0): These bits are used to select the SCI clock
source and enable or disable clock output from the SCK pin. The combination of the CKE1 and
CKE0 bits determines whether the SCK pin functions as an I/O port, the serial clock output pin, or
the serial clock input pin.
The setting of the CKE0 bit, however, is only valid for internal clock operation (CKE1 = 0) in
asynchronous mode. The CKE0 bit setting is invalid in synchronous mode, and in the case of
external clock operation (CKE1 = 1). Set CKE1 and CKE0 before determining the SCI operating
mode with SMR.
For details of clock source selection, see table 12-9 in section 12.3, Operation.
Bit 1
CKE1 Bit 0
CKE0
Description
0 0 Asynchronous mode Internal clock/SCK pin functions as I/O port
*
1
Synchronous mode Internal clock/SCK pin functions as serial clock
output
1 Asynchronous mode Internal clock/SCK pin functions as clock output
*
2
Synchronous mode Internal clock/SCK pin functions as serial clock
output
1 0 Asynchronous mode External clock/SCK pin functions as clock input
*
3
Synchronous mode External clock/SCK pin functions as serial clock
input
1 Asynchronous mode External clock/SCK pin functions as clock input
*
3
Synchronous mode External clock/SCK pin functions as serial clock
input
Notes: 1. Initial value
2. Outputs a clock of the same frequency as the bit rate.
3. Inputs a clock with a frequency 16 times the bit rate.