LAUNCHCC3220MODASF: UART parameter setting for RS-485 Modbus

Hi.

Thanks for reaching out, I am looking into this and will follow up tomorrow.

Kind Regards,

Rogelio

hi
Any update?

hi,

Now I am using UART2 library. I think MAX 485 needs RST pin. When I enable flow controller on UART2, I can't write Modbus frame Tx pin, but disabling flow controller, I get proper Modbus frame from same pin. Why does it behave this way?
 
pin configuration UART2

code snippet

void UART_test() {
// Initialize UART2 parameters
UART2_Params params;
UART2_Params_init(&params);
params.baudRate = 9600;
params.readMode = UART2_Mode_POLLING;
params.writeMode = UART2_Mode_BLOCKING;
params.readReturnMode=UART2_ReadReturnMode_PARTIAL;
// Open the UART
UART2_Handle uart;
uart = UART2_open(CONFIG_UART_RS485, &params);

// Check if UART opening was successful
if (uart == NULL) {
// Print an error message and return or handle the error appropriately
Display_printf(display, 0, 0, "Error opening UART\n");
return;
}

// Write the Modbus frame to the UART
uint8_t modbusFrame[] = {0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xC4, 0x39};
int32_t writeStatus = UART2_write(uart, modbusFrame, sizeof(modbusFrame), NULL);

if (writeStatus < 0) {
// Handle error writing to UART
Display_printf(display, 0, 0, "Error writing to UART\n");
}

// Read the response from the UART

int32_t readStatus = UART2_read(uart, buffer, BUFSIZE, &bytesRead);

if (readStatus < 0) {
// Handle error reading from UART
Display_printf(display, 0, 0, "Error reading from UART\n");
} else {
// Process the received data in 'buffer'
Display_printf(display, 0, 0, "success reading from UART\n");
Display_printf(display, 0, 0,"readbytet size %d\n", bytesRead);
// Print each byte in hexadecimal format
for (size_t i = 0; i < bytesRead; i++) {
Display_printf(display, 0, 0,"Byte %zu: 0x%02X\n", i, buffer[i]);
}
}
// Close the UART
UART2_close(uart);
}

Modbus schematic 

Hi,

You assumption is wrong. You should not use hardware flow control. You should set RTS pin manually by GPIO.

Jan

hi,
I tried RTS pin as GPIO then how to control that GPIO pin during write and red operation? .I tried to set gpio as output and make gpio high before write operation and make it low after write operation but no response from Modbus.

code snippet

GPIO_write(CONFIG_GPIO_0, 1);
// Write the Modbus frame to the UART
uint8_t modbusFrame[] = {0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xC4, 0x39};
int32_t writeStatus = UART2_write(uart, modbusFrame, sizeof(modbusFrame), NULL);
GPIO_write(CONFIG_GPIO_0, 0);

At this point, I observe that the timing digram TX and GPIO are also incorrect. Below is the actual timing diagram I observed during MAX485 communication with ESP (esps I use Tx, RX and RTS pins)

Hi,

Hard to say why you see different data output at TX line without deeper debugging. But from your image above it looks DE pin state correct.

Make sure that your DE signal have proper ahead of time before data TX (see switching characteristics from MAX485 data-sheet).  But this will not fix your issue with RX line.

Jan

hi
How to manually set RTS pin via GPIO to read and write? When I enabled flow control the Tx line received no data. If we disable receiving data on the same TX pin.

flow control disabled


flow control enabled



How to fix it?

Hi,

I think your issue is related to CTS pin when flow control is enabled. You have configured CTS pin but it is likely not used. That means UART peripheral "think" that other side is busy and not sent data. For more details how UART peripherial at CC3220 works see TRM.

Jan

hi,
When I connect launchpad Tx, Rx, RST and CST directly to the logic analyzer during the UART write operation



Why is the CST pin always high? So no data is received by TX

Hi,

What state of CTS pin did you expect, especially when is not connected to other hardware? CTS (clear to send) is a input pin at from CC3220 side.

Jan

Hi,
All pins from the launchpad connect directly to the logic analyzer, no other hardware is connected. In this case, what is the nature of the CST pin?

Hi,

Sorry, describing how RTS/CTS hardware flow control works is out of scope this forum. At internet you find many many articles at this topic.

Jan

Hi,

I have successfully tested my RS485 Modbus communication using a logic analyzer when I use a GPIO pin to control the RE & DE pins of RS485. However, I'm currently experiencing an issue where I cannot receive the Modbus response through the Rx pin on the Launchpad. When attempting to read the size of the read byte, only a single byte is displayed, and the read buffer appears to be empty. Is there a potential issue with my read function?

code snippet:

size_t bytesRead;
uint8_t buffer[25];

void UART_test() {
// Initialize UART2 parameters
UART2_Params params;
UART2_Params_init(&params);
params.baudRate = 9600;
params.readMode = UART2_Mode_BLOCKING;
params.writeMode = UART2_Mode_BLOCKING;
params.readReturnMode = UART2_ReadReturnMode_PARTIAL;
// Open the UART
UART2_Handle uart;
uart = UART2_open(CONFIG_UART_RS485, &params);
// Check if UART opening was successful
if (uart == NULL) {
// Print an error message and return or handle the error appropriately
Display_printf(display, 0, 0, "Error opening UART\n");
return;
}
while(1){
GPIO_write(CONFIG_GPIO_0, 1);
// Write the Modbus frame to the UART
uint8_t modbusFrame[] = {0x03, 0x03, 0x00, 0x00, 0x00, 0x01, 0x85, 0xE8};
int32_t writeStatus = UART2_write(uart, modbusFrame, sizeof(modbusFrame), NULL);
delayMilliseconds(8);
GPIO_write(CONFIG_GPIO_0, 0);
if (writeStatus < 0) {
// Handle error writing to UART
Display_printf(display, 0, 0, "Error writing to UART\n");
}
sleep(2);
// Read the response from the UART

uint32_t readStatus = UART2_read(uart, buffer, sizeof(buffer), &bytesRead);
Display_printf(display, 0, 0,"readbytet size %d\n", bytesRead);
if (readStatus != UART2_STATUS_SUCCESS) {
// Handle error reading from UART
Display_printf(display, 0, 0, "Error reading from UART\n");
} else {
// Process the received data in 'buffer'
Display_printf(display, 0, 0, "success reading from UART\n");
// Print each byte in hexadecimal format

Display_printf(display, 0, 0," data: %x\n", buffer[1]);
Display_printf(display, 0, 0," data: %x\n", buffer[2]);
Display_printf(display, 0, 0," data: %x\n", buffer[3]);
Display_printf(display, 0, 0," data: %x\n", buffer[4]);
Display_printf(display, 0, 0," data: %x\n", buffer[5]);
Display_printf(display, 0, 0," data: %x\n", buffer[6]);
Display_printf(display, 0, 0," data: %x\n", buffer[7]);

}
sleep(5);
}
// Close the UART
UART2_close(uart);
}

console log:

readbytet size 1
success reading from UART
data: 0
data: 0
data: 0
data: 0
data: 0
data: 0
data: 0

logical analyzer:



pin configuration:

hi
Any update?

hello,
any Update?