HD64F38024HV Datasheet, PDF (406/684 Pages) Renesas Technology Corp – Hardware Manual Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Super Low Power Series

Section 10 Serial Communication Interface
8. Transmit and receive operations when making a state transition
Make sure that transmit and receive operations have completely finished before carrying out state
transition processing.
9. Switching SCK₃₂ function
If pin SCK₃₂ is used as a clock output pin by SCI3 in synchronous mode and is then switched to a
general input/output pin (a pin with a different function), the pin outputs a low level signal for half
a system clock (φ) cycle immediately after it is switched.
This can be prevented by either of the following methods according to the situation.
a. When an SCK₃₂ function is switched from clock output to non clock-output
When stopping data transfer, issue one instruction to clear bits TE and RE to 0 and to set bits
CKE1 and CKE0 in SCR3 to 1 and 0, respectively. In this case, bit COM in SMR should be
left 1. The above prevents SCK₃₂ from being used as a general input/output pin. To avoid an
intermediate level of voltage from being applied to SCK₃₂, the line connected to SCK₃₂ should
be pulled up to the V_CC level via a resistor, or supplied with output from an external device.
b. When an SCK₃₂ function is switched from clock output to general input/output
When stopping data transfer,
(i) Issue one instruction to clear bits TE and RE to 0 and to set bits CKE1 and CKE0 in SCR3
to 1 and 0, respectively.
(ii) Clear bit COM in SMR to 0
(iii) Clear bits CKE1 and CKE0 in SCR3 to 0
Note that special care is also needed here to avoid an intermediate level of voltage from being
applied to SCK₃₂.
10. Set up at subactive or subsleep mode
At subactive or subsleep mode, SCI3 becomes possible use only at CPU clock is φw/2.
11. Oscillator use with serial communications interface (H8/38124 Group only)
When implementing the serial communications interface on the H8/38124 Group, the system
clock oscillator must be used. The on-chip oscillator should not be used in this case. See on-chip
oscillator selection method in section 4.2, System Clock Generator, for information on switching
between the system clock oscillator and the on-chip oscillator.
Rev. 8.00 Mar. 09, 2010 Page 384 of 658
REJ09B0042-0800