imx28 AUART Baudrate / Hispeed /clock

[wolfgang_gaerbe]

Hi,

We (want to) use AUART module with 3.25MBs - as this is indicated as maximum speed in the reference manual p.1937.

According to this manual p.1939 - the proper divisor is:

24M x 32 / 3250000 = 236 = 0xEC - the smallest divisor allowed.

Writing this divisor in BAUD_DIVFRAC and BAUD_DIVINT - we got the following behaviour:

TX operates on any divisor setting between dec. 224 - dec 239 wiht 3.4MBps.

It really looks like the lowest 4 Bits of BAUD_DIVFRAC have no influence on the TX clock.

Otherwise it seems that this bits are used for RX clock - and then it makes a difference.

1.) Is there a document which describes TX clock / RX clock in detail ?

2.) There are 2 indications of a "HISPEED" mode in the manual - and a bit which gives details  in the status register.

Is there a document describing HISPEED mode ?

rgds.

[Yuri]

Hello,

1.

  Please refer to sections 24.2.1 (Fractional Baud Rate Divider)
and 30.2.1 (Fractional Baud Rate Divider) of the i.MX28 RM

about UART clock calculations.

http://cache.nxp.com/files/dsp/doc/ref_manual/MCIMX28RM.pdf

You wrote, that low 4 bits of BAUD_DIVFRAC do not influence

of the speed ; note - 0xEC is the lowest allowed value and low bits

influence really is hard to detect. 

2.

The HISPEED bit field is used to indicate if UART IP supports hi-speed

mode.

Have a great day,
Yuri

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------