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 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). The CKE1 and CKE0 bits must be set before determining
the SCI’s operating mode with SCSMR1.
For details of clock source selection, see table 15.9 in section 15.3, Operation.
Bit 1: CKE1
Bit 0: CKE0
Description
0
0
Asynchronous mode
Internal clock/SCK pin functions as
1
*
input pin (input signal ignored)
Synchronous mode
Asynchronous mode
Synchronous mode
Asynchronous mode
Synchronous mode
Asynchronous mode
Synchronous mode
Internal clock/SCK pin functions as
1
*
serial clock output
1
0
1
Internal clock/SCK pin functions as
2
*
clock output
Internal clock/SCK pin functions as
serial clock output
1
External clock/SCK pin functions as
3
*
clock input
External clock/SCK pin functions as
serial clock input
External clock/SCK pin functions as
3
*
clock input
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.
Rev. 6.0, 07/02, page 604 of 986
RENESAS [ RENESAS TECHNOLOGY CORP ]
