8-bit MicrocontrollersのトピックRe: Simple SCI Polling Receive and Transmit Code

Simple SCI Polling Receive and Transmit Code

datamstr — Sat, 30 Dec 2006 09:19:01 GMT

Hi All,

I am using the MC908QB8 Demo Board and CW50. I have read through the manual and looked through the posts on this forum for help. I am trying to simply poll the SCI register for an incoming char and then transmit it out the SCI port. My code is listed below, as far as I understand the steps are:

1. Check for the SCI Recevier Full Flag. (SCRF)

2. Read the SCI Data Register

3. Check for the SCI Transmitter Empty flag. (SCTE)

4. Write the SCI Data Register

// SCI Loop Test
for(; /* loop forever */
{
__RESET_WATCHDOG(); /* feeds the dog */

   if(SCS1_SCRF) // SCRF Bit - Check for char ready and clear bit
     {
     RChar = SCDR; // Get SCI Char

     while(!SCS1_SCTE) //SCTE Bit - wait for transmitter empty
       ;
       SCDR = RChar;   // Send SCI char
     }
   }

My code is not working, any help please?

Thanks,

David Evennou

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sat, 30 Dec 2006 09:49:05 GMT

Try removing the jumper from the COM EN block (near the RS232 connector).

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sat, 30 Dec 2006 10:33:17 GMT

My configuration is:

1. SCI receive jumper (Lin/Com) is removed.

2. SCI input data is from an RS-485 Transceiver IC

3. Transmit jumper is on the COM side and the DB9 connector is plugged into the PC using HyperTerminal.

4. The transmit side works OK, I can send a character to the HyperTerminal running at 9600 Baud

5. Receive data is from a single board computer sending serial data to the RS-485 IC.

To validate this setup, I connected the output from the RS-485 IC to the COM pin on the Demo Board.

The serial string of characters flows through to HyperTerminal just fine.

So, that is whay I think I must be doing something wrong in the code.

Thanks,
David

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sat, 30 Dec 2006 12:37:43 GMT

datamstr wrote:
[snip.....] To validate this setup, I connected the output from the RS-485 IC to the COM pin on the Demo Board.
The serial string of characters flows through to HyperTerminal just fine.
So, that is whay I think I must be doing something wrong in the code.
Thanks,
David

Sorry, I first read this as a 9S08QG8 demo board. So, the following comments/questions:

1. Are the LIN/COM jumpers installed between pins 1&3 (xmit) and 2&4 (rcv)?
2. By "COM pin", do you mean pin #3 of the RS232 connector? If so, can you scope J1-7 to see if you have the Rx signal there?
3. Check the pins on the ICL3232 (com) chip to make sure they are on the solder pads and are making good connections.

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sat, 30 Dec 2006 19:20:13 GMT

Hi,

1. I have one LIN/COM jumper installed between Pins 1 & 3. (for RS-232 xmit data)

2. I am referring to the LIN/COM Pin 4. (SCI Rx) This pin is wired to the external RS-485 Transceiver Output.

3. The pins of the ICL3232 are connected.

Thanks,

David

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sat, 30 Dec 2006 23:10:52 GMT

Since you are bypassing the ICL3232, the signal will not be inverted at the '08 input pin. This means a valid "start" bit will not be detected. Also, the RS485 voltage levels should be constrained to those limits of the '08 inputs (TTL/CMOS)--a function that is also normally handled by the ICL3232. As a test, you could install the jumper (2&4) on the COM SEL block and input the signal at pin #3 on the RS232 connector.

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sat, 30 Dec 2006 23:49:32 GMT

Actually, the signal polarity is correct from the MAX3280 RS-485 Receiver to the SCI Rx pin and it is running at 5 VDC as well as the QB8. I confirmed this by connecting the MAX3280 Output to the ICL3232 Driver (COM SEL Pin 1) and monitoring the serial data using HyperTerminal. The RS-485 voltage level is at 5 VDC.

I like your suggestion to connect the SCI Rx pin to the ICL3232 (COM SEL jumper pins 2 & 4). I should be able to do a loopback test from HyperTerminal, the QB8 can echo back what I type into HT.

Thanks,

David

Re: Simple SCI Polling Receive and Transmit Code

bigmac — Sun, 31 Dec 2006 00:12:00 GMT

Hello David,

From your description, I assume the other single board computer (that generates the serial data for the demo board to receive) has a RS-485 driver fitted. Using an oscilloscope, can you actually observe the presence of data at the receiver output pin of the local RS-485 device, i.e. receive mode is enabled. If so, you may need to swap the differential input connections to achieve correct polarity into the QB8 RxD pin.

Also note that the baud rate for the received data will need to be the same rate as for the data forwarded to the PC.

You may find it more convenient for initial testing of code, to add a jumper so that the incoming data originates from the PC, rather than the SBC. Then any character typed at the keyboard should simply be echoed.

Regards,

Mac

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 00:45:28 GMT

Hi Mac,

That is correct, the SBC has a RS-485 Driver. I swapped the differential inputs just to try it, but still not getting data to the SCI. The baud rate should be correct for both xmit and receive. I used the settings I received from a Freescale Support Request a couple of months ago. The Device Initialization Inspector in CW50 shows the baud rate as 9638.5542. My next step is to try loopback using the RS-232 and HyperTerminal. Do you know if there is a program already written to run this test?

Also, I not yet figured out how to use breakpoints in CW50 with the QB8 Demo Board.

Thanks,
David

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 02:42:00 GMT

OK, I am using only the QB8 Demo Board RS-232 with both jumpers installed for COM SEL (1 & 3, 2 & 4).

Using the same code I originally posted, still nothing back from the SCI. I can't really tell if the SCI Data Register has anything in it. I think the next step is to try to send a character from the SCI Tx to RS-232 port first. (reverse the order)

Thanks,

David

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 03:02:37 GMT

OK, Good News! I plugged in the code below and that works OK, got characters in HyperTerminal.

So now, how can I get the SCI Rx working?

Thanks,
David

void MCU_init(void); /* Device initialization function declaration */

void Delay(byte time);

void main(void) {

MCU_init(); /* call Device Initialization */

for(; {

while(!SCS1_TC); SCDR = 0x55;

Delay(5);

} /* loop forever */

}

void Delay(byte time)

{

word i;

for(i = 0;i < time*255; i++)

{

__RESET_WATCHDOG();

}

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sun, 31 Dec 2006 05:16:27 GMT

David,
Hey, your 1/2 way there!
This is just a suggestion, but when bringing up any new board or feature, I disable the watchdog timer to eliminate a variable from the debugging equation. Especially when there are wait loops anywhere in the code.

Also, don't forget to set the RE bit in SCC2 to enable the receiver.

Frank

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 06:15:08 GMT

Frank,

Here is my MCUInit code ......no interrupts, Transmitter and Receiver Enabled, SCI Enabled.

/* ### Init_SCI init code */
/* SCIACTL: AM1=0,ALOST=0,AM0=0,ACLK=0,AFIN=0,ARUN=0,AROVFL=0,ARD8=0 */
SCIACTL = 0x00;
/* SCPSC: PDS2=0,PDS1=0,PDS0=1,PSSB4=1,PSSB3=0,PSSB2=0,PSSB1=1,PSSB0=1 */
SCPSC = 0x33;
/* SCC3: R8=0,T8=0,ORIE=0,NEIE=0,FEIE=0,PEIE=0 */
SCC3 = 0x00;
/* SCBR: LINT=0,LINR=0,SCP1=1,SCP0=0,SCR2=0,SCR1=0,SCR0=1 */
SCBR = 0x21;
/* SCC1: LOOPS=0,ENSCI=1,TXINV=0,M=0,WAKE=0,ILTY=0,PEN=0,PTY=0 */
SCC1 = 0x40;
/* SCC2: SCTIE=0,TCIE=0,SCRIE=0,ILIE=0,TE=1,RE=1,RWU=0,SBK=0 */
SCC2 = 0x0C;

Config Registers - (COP is Disabled)

/* Common initialization of the write once registers */
/* CONFIG1: COPRS=0,LVISTOP=0,LVIRSTD=0,LVIPWRD=0,LVITRIP=0,SSREC=0,STOP=0,COPD=1 */
CONFIG1 = 0x01;
/* CONFIG2: IRQPUD=0,IRQEN=0,ESCIBDsrc=0,OSCENINSTOP=0,RSTEN=0 */
CONFIG2 = 0x00;

Thanks,
David

Re: Simple SCI Polling Receive and Transmit Code

peg — Sun, 31 Dec 2006 07:02:49 GMT

Hi David,

I am right at this moment writing a protocol translator using both SCI ports of a 9S08GT16.

This is to allow two incompatible pieces of equipment to talk to one another.

One side is two wire 485 9600 baud and the other is 4 wire 19200 and the protocol is completely different.

So all this stuff is right in my head now.

At this point I can see nothing wrong with what you are doing and so would suggest that you have a hardware issue.

What I did is this:

Replace one side with a PC running a terminal emulator.

Write some code to send a string to the PC when the device is reset using the same mechanisms in the code that will be used by the application. This tests many things before you get started. Most SCI setup including baudrate and your PC terminal setup etc.

You should only need:

Enable SCI

enable tx and rx

set baudrate

which you seem to have.

Can you test for the presence of data right at the MCU pin input?

Even if the baudrate is a bit off or parity wrong or whatever you generally will get some rubbish occasionally if you throw enough data at it. Maybe get your terminal emulator to sent a small file at your MCU to see if you can recieve anything at all.

Even if you only have a multimeter you can put it on the RDI pin (it should idle high) then type at the terminal as fast as you can, you should see a small drop in voltage as the data passes. I just tested this, I saw 3.28 idle and 3.24 with data. Sendig a file drops it to below 2 volts.

Hope this helps

Regards

David (Peg)

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sun, 31 Dec 2006 08:16:04 GMT

David,

What is your clock source? Assuming you want to use the internal clock and you want a baud rate of 9600, you should initialized the OSCSC register for 12.8MHz ( ICFS1:ICFS0 = 10) for the register values you've chosen to work out to 9600. Otherwise, the reset value will give you a 4.0MHz clock.

Frank

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 08:27:32 GMT

Hi Frank,

The following information from Freescale Support is what I am using:

When using internal oscillator it is not possible to set internal bus
frequency to 4.9152 Mhz.
You can for example set the bus frequency to 3.2MHz and set the ECSI
prescallers following way

For 9600Bd
ESCI baud rate clock source = CGMXCLK,
Prescaler divisor = 2,
Prescaler divisor fine adjust = $13
Baud rate prescaler = 4
Baud rate divisor = 2

Thanks,
David

Re: Simple SCI Polling Receive and Transmit Code

thisobj — Sun, 31 Dec 2006 09:11:20 GMT

David,

That info is correct. But I don't think you'll get a 3.2MHz bus frequency unless you select the internal 12.8MHz clock, since Bus Clock = CGMXCLK/4. Since you're selecting CGMXCLK as the ESCI clock source, it needs to be init'd to 12.8MHz by setting the bits in OSCSC. This is called out in the document, MC68HC08QB8.pdf on page 100.

Frank

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 09:40:46 GMT

Hi Frank,

Thanks for pointing that out to me. I remember now that the email from Freescale Support had that error, so I changed to internal clock. I just reviewed my settings in the CW Inspector and the Clock Source is set to Internal and the Internal Oscillator Frequency is 12.8 MHZ. The internal Bus Clock is set to 3.2 MHZ.

Sorry about that.

Thanks,

David

Re: Simple SCI Polling Receive and Transmit Code

peg — Sun, 31 Dec 2006 09:58:24 GMT

Hi David,

You said earlier that you could send from the MCU to a terminal on a PC so as the Tx and Rx baudrate is the same I believe that the clock/baudrate divisor must already be OK!

I don't know your hardware and as everything else seems OK that is why I was suspecting that the data is not actually getting into the MCU.

Have you confirmed this?

Regards

Peg

Re: Simple SCI Polling Receive and Transmit Code

datamstr — Sun, 31 Dec 2006 10:47:21 GMT

Hi Peg,

I just got back to the testing and I do have data at the MCU Rx pin. The DVM voltage drops when I hold down a key in HyperTermminal. Also, the hardware is just the Demo Board.

Anything I can try in code?

Thanks,
David