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How to Set SCI TE/RE Bit

Last Updated:07/04/2018

Question:

The SCIx.TE bit can be written with "1", but the SCIx.RE bit cannot. (or the SCIx.RE bit can be written with "1", but the SCIx.TE bit cannot)
What is wrong?

Answer:

The following restrictions are described in the user's manual.

SCI and SCIa
 1 can be written only when TE = 0 and RE = 0. 
 After setting TE or RE to 1, only 0 can be written in TE and RE.

SCIb
 While the SMR.CM bit is 1, 1 can be written only when TE = 0 and RE = 0. 
 After setting TE or RE to 1, only 0 can be written in TE and RE.
 While the SMR.CM bit is 0, bits are writable at any timing.

SCIc, SCId, SCIe, SCIf, SCIg, SCIh, and SCIi
 1 can be written only when TE = 0 and RE = 0, while the SMR.CM bit is 1. 
 After setting TE or RE to 1, only 0 can be written to TE and RE. While the SMR.CM bit is 0 and the SIMR1.IICM bit is 0, writing is enabled under any condition.

Due to the above restrictions, to set TE or RE back to 0, it is necessary to set both TE and RE to 0 at the same time.
In order to set 1, it is necessary to write it when the both TE and RE bits are 0.
Follow the restrictions on the user's manual strictly for SCIx.TE and SCIx.RE settings.

Suitable Products
RX Family