H838532H datasheet(359/508 Pages) RENESAS

359 / 508 page

Section 10 Serial Communication Interface

Rev. 1.00 May 30, 2008 Page 339 of 484

REJ09B0436-0100

(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 SCK

3x Function

If pin SCK

3x 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 SCK

3x 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 SCK

3x from being used as a general input/output pin. To avoid an

intermediate level of voltage from being applied to SCK

3x, the line connected to SCK3x should

be pulled up to the V

CC level via a resistor, or supplied with output from an external device.

b. When an SCK

3x 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 SCK

3x.

(10) Setup at Subactive or Subsleep Mode

At subactive or subsleep mode, SCI3 becomes possible use only at CPU clock is

φw/2.

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