topic Re: LPC1518 RS485 master mode (9th bit) in LPC Microcontrollers

LPC1518 RS485 master mode (9th bit)

jeroenbussink — Wed, 08 Mar 2017 13:29:19 GMT

Hello,

How can I set the 9th bit when sending data with a LPC1518,?

On the LPC1830 I have used the sticky parity for this but I can't find this for the LPC 1518.

BR,

Jeroen

Re: LPC1518 RS485 master mode (9th bit)

kerryzhou — Thu, 09 Mar 2017 10:30:01 GMT

Hi Jeroen Bussink,

If you want to set the 9 bit mode, you can select the DATAEN as 0x02, just like the user manual:

Wish it helps you!

If you still have question, please let me know!

Have a great day,
Kerry

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Re: LPC1518 RS485 master mode (9th bit)

jeroenbussink — Thu, 09 Mar 2017 10:41:46 GMT

Hi Kerry,

Thanks for you answer, the things you point out I already set.

But my question is how do I set the 9th bit to 1 so the LPC1518 will send data with the 9th bit set to 1.

In our protocol we send out the first byte (address) with the 9th bit set to 1 and the rest of the bytes with the 9th bit 0, so the slave device knows when a address byte is received.

On the LPC1830 I set the sticky parity to 1 or 0.

BR,

Jeroen

Re: LPC1518 RS485 master mode (9th bit)

kerryzhou — Mon, 13 Mar 2017 10:15:50 GMT

Hi Jeroen Bussink,

I think maybe you misunderstanding the 9bit function in the LPC15xx.

Multiprocessor/multidrop (9-bit) mode with software address compare.

From the user manual, this 9bit is just used for the address compare, you can consider the MSB=1 when set the 9bit mode, it normally used for the address compare, the data sending may don't have the 9 bit function.

Wish it helps you!

Have a great day,
Kerry

Re: LPC1518 RS485 master mode (9th bit)

chrispflieger — Thu, 05 Oct 2017 21:21:22 GMT

You need to write it as a word and not as a byte. I.e. any value over 255 will have the ninth bit set.

I can't remember if the current CMSIS code treats it as a word or if I wrote my own function in there to allow it. Some of the code cast the value as a uint8_t which chops off that ninth bit.