Renesas H8S/2319 series Hardware Manual page 464

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 Bit 0
CKE1 CKE0 Description
0 0 Asynchronous mode
Synchronous mode
1 Asynchronous mode
Synchronous mode
1 0 Asynchronous mode
Synchronous mode
1 Asynchronous mode
Synchronous mode
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.
Rev. 5.00, 12/03, page 434 of 1088
Internal clock/SCK pin functions as I/O port *
Internal clock/SCK pin functions as serial clock
output
Internal clock/SCK pin functions as clock output *
Internal clock/SCK pin functions as serial clock
output
External clock/SCK pin functions as clock input *
External clock/SCK pin functions as serial clock
input
External clock/SCK pin functions as clock input *
External clock/SCK pin functions as serial clock
input
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