MM9Z1_638 SCI Half-Duplex mode, RDRF not set

joek — Thu, 07 Jan 2016 08:39:41 GMT

Hello,

The MM9Z1_638 has an S12Z processor and S08SCIV4 SCI module. I want to use the SCI in one-wire, half duplex mode. The physical pin I am using is the LIN pin. So, I have set both LIN_TX.FROMSCI and LIN_RX.TOSCI. I have a terminal application running on my PC and a USB-LIN adapter connected (19,200 baud, N, 8, 1).

I can send data from the processor to the terminal with no problems. But, I cannot receive any data. RDRF is never set. I do see RXEDGIF set when I send a character. This implies the signal is making it to the SCI module. I have checked the baud rate settings and confirmed that a sent character (e.g. 'U') has exactly the same scope waveform on the LIN pin as a received character. So I think the baud rate setting is OK. I did find a bug in the MM9Z1_638 example code in this area, but fixed it (baud rate was off by 2.5%).

All SCI interrupts are disabled. I want it to work via polling first, then I will implement the interrupts. I believe I should be able to send a character from the terminal to the LIN pin and see RDRF set.

I think I need to have LOOPS=1 and RSRC=1 for one-wire mode. In the process of debugging, I cleared RSRC=0 to see what would happen. It turns out that in this mode (internal loopback) when I send a character by writing to SCID, the receiver sets RDRF. Great! But as soon as I set RSRC=1, RDRF never sets.

Here is the SCI initialization code:

void SCIInit(void) {

B_SCIBD = (u16)(25ul*1000000ul/SCI_BAUD/16ul);

B_SCIC1 = B_SCIC1_DPD1_MASK | B_SCIC1_DPD0_MASK | B_SCIC1_LOOPS_MASK | B_SCIC1_RSRC_MASK;

B_SCIC2 = B_SCIC2_TE_MASK|B_SCIC2_RE_MASK; // enable rx and tx

B_SCIC3 = 0x00;

}

And here is the receive function I call repeatedly from the main loop:

char SCIRec(void) {

if (B_SCIS1_RDRF) {

return B_SCID;

}

else {

return 0x00;

}

I send characters from the terminal to the LIN pin and the debugger will never break on "return B_SCID;", but if I halt execution I can see RXEDGIF has been set. If I modify the above code to clear RSRC (internal loopback mode) and send a character by writing to SCID, then the debugger will break on the "return B_SCID;" line.

Thank you for your help!

Re: MM9Z1_638 SCI Half-Duplex mode, RDRF not set

joek — Thu, 07 Jan 2016 21:57:46 GMT

The problem has been resolved. I was mistaken to set LOOPS=1 and RSRC=1. This should only be done when using SCI one-wire mode on a GPIO pin.

The LIN PHY connects tx and rx internally, so LOOPS and RSRC should both be 0. If the receiver is enabled it will see every byte transmitted.

S12 / MagniV MicrocontrollersのトピックMM9Z1_638 SCI Half-Duplex mode, RDRF not set

MM9Z1_638 SCI Half-Duplex mode, RDRF not set

Re: MM9Z1_638 SCI Half-Duplex mode, RDRF not set