TL16C754C:How to set TLR regsiter in TL16C754C controller

GSR,

To access the TLR register you must first set EFR[4]=1 and MCR[6]=1.

Some delay may be required before reading the THR because it takes some time for the serialization of the data and for the transmitter status bits to update in the LSR. For the standard registers you can program them in any order but some enhanced registers like the TLR require bits to be set in other registers before you can access them.

To dump the readable registers you can use the inportb command

/* Comm Port 1 or A -- UART register set definition */
#define RBR_UART1      0x300  /*Receiver Buffer Register of chA */
#define THR_UART1      0x300  /*Transmitter Holding Register of chA */
#define IER_UART1      0x301  /*Interrupt Enable Register of chA */
#define IIR_UART1      0x302  /*Interrupt Identify Register of chA */
#define FCR_UART1      0x302  /*FIFO Control Register of chA */
#define LCR_UART1      0x303  /*Line Control Register of chA */
#define MCR_UART1      0x304  /*Modem Control Register of chA */
#define LSR_UART1      0x305  /*Line Status Register of chA */
#define MSR_UART1      0x306  /*Modem Status Register of chA*/
#define SPR_UART1      0x307  /*Scratch Pad Register of chA */
#define DLL_UART1      0x300  /*Divisor Latch LSB of chA */
#define DLM_UART1      0x301  /*Divisor Latch MSB of chA */
/* End Comm Port definition */

main(
 

 // read registers 
 /* Port 1 - Channel A */

 inportb(LCR_UART1);         /* read RHR*/
 outportb(LCR_UART1, 0x00)   /* set LCR[7]=0 */
 inportb(IER_UART1);         /* read IER*/
 inportb(IIR_UART1);         /* read IER*/
 inportb(MCR_UART1);         /* read MCR*/
 inportb(LSR_UART1);         /* read LSR*/ 
 inportb(MSR_UART1);         /* read MSR*/     
 inportb(SPR_UART1);         /* read scratch pad register*/
}
/* end of main */

My bench setup uses MS-DOS so I can directly access the registers with debug commands and scripts.

Best Regards,

Joe