Help understanding the SC16IS740 datasheet. SPI to UART registers

[dweinho1]

Hi all, I am back with a simple question. I am using a pyboard to communicate with a six devices over UART. Of course it only has five UARTs available so I am using a breakout board with a SC16IS740 SPI to UART converter. https://www.digikey.com/en/products/det ... 49/9960305

I am not getting it to respond the way I expect it to and need help to confirm I am reading the datasheet correctly. Here is the datasheet: https://www.nxp.com/docs/en/data-sheet/ ... 50_760.pdf
The list of registers is on page 21.

I am trying to do the following:
- Write to the LCR register (0x03)--allow setting the special registers, set parity to none, stops bits to 1, and data bits to 8.
- Write the special registers (0x00 and 0x01)--set a divisor of 12 for 9600 baud rate
- Write to the LCR register again
- Read the RCR register (0x00)

So I am sending the following (binary and hex):
- LCR register write: 0001 1000 1000 0011: 0x18 0x83
- DLL register write: 0000 0000 0000 1100: 0x00 0x0C
- DLH register write: 0000 1000 0000 0000: 0x08 0x00
- LCR register write: 0001 1000 0000 0011: 0x18 0x03
- RCR register read: 1000 0000: 0x80

I also believe the polarity and phase are both 0 based on page 43.

Does this look correct?

[dweinho1]

As a little update in case anyone searches for the SC16IS740 in the future.

I am getting reading and writing registers at this point but it is intermittent. Seems like I am going to have to break down and get a logic analyzer.

Meanwhile I am doing the following (basically what I wrote above):

Code: Select all

LCR_register_read = '10011000' 
LCR_register_write = '00011000'
LCR_init = '10000011' # unlocks the "special registers"--DLL and DLH--that allows setting the baudrate
LCR_deinit = '00000011' #locks the special registers; also setting parity to none, stop bit to 1, and data bits to 8

DLL_write = '00000000'
DLL_value = '00001100' #sets baud rate to 9600 based on 1.8432 MHz crystal

I am then also writing to the transmit register and monitoring the serial port with tera term and USB to serial converter. I am not seeing anything. This is the converter (though not that it matters) https://www.usbgear.com/USBG-232MINI.html
I need to try swapping the lines but right now I don't have anything to do that.