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Peripheral Simulation

For Cadence Design Systems Inc. R8051XC2-B (2 DPTR) — Serial UART 1

Simulation support for this peripheral or feature is comprised of:

  • Dialog boxes which display and allow you to change peripheral configuration.
  • VTREGs (Virtual Target Registers) which support I/O with the peripheral.

These simulation capabilities are described below.

Serial Channel-1 Dialog

Serial Channel-1

The Serial Channel 1 dialog displays and allows you to edit the configuration of the Serial Interface.

  • Mode displays and allows you to change the serial interface mode of operation (data bit length and baud rate).
  • S1CON (Serial Control Register) holds the control and setup information for programming serial port 1.
  • S1BUF (Serial Interface Buffer Register) contains the transmit data to be sent or received data.
  • SM21 (Enable Serial Port 1 Multiprocessor Communication In Modes 2 and 3) is set to suppress a receiver interrupt (RI1) if the received 9th data bit is 0.
  • TB81 (Serial Port 1 Transmitter Bit 9) is the 9th data bit to be transmitted for serial modes 2 and 3.
  • REN1 (Serial Port 1 Receiver Enable) is set to enable serial data input.
  • RB81 (Serial Port 1 Receiver Bit 9) is set for serial modes 2 and 3 when a 9th bit is received. In serial mode 1, this is the stop bit.


  • S1RELH (Baudrate Reload High)
  • S1RELL (Baudrate Reload Low)
  • Baudrate is the actual baud rate for the serial channel.


  • TI1 (Transmitter Interrupt Flag) is set by hardware for each character frame transmitted. TI1 is cleared by software.
  • RI1 (Receiver Interrupt Flag) is set by hardware for each character frame received. RI1 is cleared by software.

Data Type: unsigned int

The SIN VTREG represents the serial input of the simulated microcontroller. Values you assign to SIN are input to the serial channel. You may assign input using the command window. For example,


causes the simulated microcontroller serial input to receive the ASCII character A. If you want to use the SIN VRTEG to simulate reception of multiple characters, you must be sure to delay for atleast one character time between successive assignments to SIN. This may be done using a signal function. For example:

signal void send_cat (void) {
swatch(0.01);  /* Wait 1/100 seconds */
SIN='C';       /* Send a C */

You may use the SIN VTREG to input more than 8 bits of data. For example,


inputs a 9-bit value. This is useful if you use 9-bit serial I/O. In addition to the SIN VRTEG, the serial window allows you to input serial characters by simply typing. Serial characters that are transmitted byt the simulated microcontroller appear in the serial window.

Data Type: unsigned int

The SOUT VTREG represents the serial output from the simulated microcontroller. Whenever the simulated serial port transmits a character, the value transmitted is automatically assigned to SOUT (which is read-only). You may read the value of SOUT to determine the character transmitted by your simulated program. For example,


outputs the value of the last character transmitted. You may use the SOUT VTREG in a script to process transmitted data. For example,

signal void sout_sig (void) {
while (1)
  wwatch(SOUT);     /* wait for something in SOUT */
  printf ("Transmitted a %2.2X\n", (unsigned) SOUT);
Get more information about the
Peripheral Simulation Capabilities
of the µVision Debugger.
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