SC16IS740 I2C configuration

[buol]

Hello,

I am trying to use the SC16IS740 chip in order to read a periodically & single-character sending UART device via I2C from an embedded linux module. In a first step I would just like to read the characters manually using i2ctools, without interrupts or FIFO. However, I'm not sure if I do the configuration correctly.

UART specification: Baud 9600, 8bit word lengt, no parity, 1 stop bit
Crystal: 1.8432MHz

Configuration sequence:
i2cset -y 2 0x4d 0x18 0x80   # LCR - access special registers
i2cset -y 2 0x4d 0x00 0x0C   # DLL - divisor 0x000C (12) to get baud 9600
i2cset -y 2 0x4d 0x08 0x00   # DLH - divisor 0x000C (12) to get baud 9600
i2cset -y 2 0x4d 0x18 0x03   # LCR - access general registers, set config 8N1
i2cset -y 2 0x4d 0x10 0x00   # FCR - disable FIFO (default..)
i2cset -y 2 0x4d 0x08 0x00   # IER - disable interrupts(default..)
(note: register addresses are shifted by one compared to the datasheet)

By now I think I should be able to read the character sent by my UART device in the RHR register and see the LSR[0] flag set. However, RHR is constantly at 0x04 and the LSR[0] flag cleared.

Am I missing something in my configuration sequence so far or am I probably facing a hardware issue?

Thanks for every advice
Oliver

[david_diaz]

Hello Oliver,

I hope all is great with you.

In this case, I would like to recommend the example project below. At the example mentioned, you may find an initialization of the device that can be useful for you.

SC16IS752 - Bare metal example project

I hope the information provided was useful for you. Please let me know if you have any further question.

Regards,

David

[buol]

Hello David

Thanks for your input. I've seen similar initializations in some application notes before and as you can see adapted my approach to it. However since I don't want to use interrupts of FIFO yet, I don't think I need enhanced functions etc.

Regards,
Oliver

[darioarias]

Hi Oliver,

If you are not using interrupts how do you know when there is data available? Are you constantly polling the LSR[0]? The configuration you used is correct, maybe you could share with us a fragment of the code to try to find why you can't read from RHR register.

Darío

[buol]

Hello Dario,

Thanks for the confirmation. For the moment I work just with manual commands, no code.

The UART device on the other side sends periodically (~50Hz) one character (from a set of 8 possible characters). I figured, I should be able to read this with a randomly timed, manual register read, but I see your point with the interrupts.

How is the chip supposed to work in this case?

Regards,

Oliver