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Parallel Port

In an embedded system a microprocessor is used to control parts of a system, and this may involve sending and receiving logic signals via a parallel port. The MCF5206 parallel ports are explained in detail in the documentation; however, the registers for controlling Port A are as follows:

Register	Address
MBARx	0x1000 0000	module base address
PADDR	MBARx + 0x01C5	Port A data dir. reg., 8 bit, r/w
PADAT	MBARx +0x01C9	Port A data reg., 8 bit, r/w

Read: DDR=0, write DDR=1

Let's look at an example of how to use Port A for TTL logic i/o. Download the assembly program porta1s.s:

/*    porta1s.s
      test of port a parallel i/o
*/
	
      .text
      .even
      .global     main
main:
      move.b      #0xff,%d1          /* set port A */
      move.b	  %d1,PADDR          /* for output */
      move.b      #0b10101011,%d1
      move.b      %d1,PADAT          /* write something to port A*/
      rts

MBARx      =      0x10000000     /* Module Base Address value */
PADDR      =      MBARx+0x01C5   /* Port A Data Direction Register, ;8-bit, R/W */				    	
PADAT      =      MBARx+0x01C9   /* Port A Data Register, 8-bit, R/W */

Examine this code carefully, and notice:

• The two registers controlling Port A are specified as offsets from the module base address (recall the memory map Figure 53).

• The 8-bit data direction register PADDR is loaded with 1's to set port A for output. (In general, each bit can be programmed individually for either input or output).

• The 8-bit data register PADAT is loaded with the desired output data.

Exercise.

1.

Make the necessary hardware connections, including ground. Refer to the Appendix 18.5 describing the SBC cable pins.

2.

Assemble and link the program.

3.

Load the program porta1s.x into the SBC.

4.

Run the code:

go 10000

5.

Use an osilloscope to measure the voltages at each port location. Check for correctness.

A C version is available in the file

porta1c.c:

/* porta1c.c
   test of sbc port a */


#define  MBARx   0x10000000         /* Module Base Address value */
#define  PADDR  (* (char *)  (MBARx+0x01C5))  
           /* Port A Data Direction Register, ;8-bit, R/W */	
#define  PADAT  (* (char *)  (MBARx+0x01C9))  
          /* Port A Data Register, 8-bit, R/W */

int   main() {
  
   PADDR = 0xff;          /* set port A for output */
   PADAT = 0xaa;          /* output something */

   return  0;
}

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