SLAS191A Datasheet, PDF (67/86 Pages) Texas Instruments – Starter Kit Evaluation Kit Manual

5 Half Duplex Monitor Software UART
The Monitor Program provides several functions for handling serial data communications using the RS-232
interface. The user can call these functions by using the associated vectors in the terminal program. Use
the absolute address mode to call these functions. For example, a possible syntax for preparing the half
duplex software UART to receive characters is:
CALL &0FFD6h ;in address FFD6h the vector of RX_Prep is stored
another possible syntax is:
RX_Prep .equ
0FFD6h
CALL &RX_Prep ;in address FFD6h the vector of RX_Prep is stored
The STK/EVK software UART cannot be used for binary transfers for the following two reasons:
• The protocol has only seven data-bits.
• A zero cannot be received because this is the detection scheme for no-character-received.
The vectors related to these functions are stored in the following locations (see Table 5–1):
Table 5–1. Function/Vector
FUNCTION NAME VECTOR ADDRESS
FUNCTION PURPOSE
TX_Word
TX_Char^†
TX_Table^†
RX_Prep^†
TX_Prep^†
0FFD0h
0FFD2h
0FFD4h
0FFD6h
0FFD8h
Transmit 1 space and a four digit hex number in R11
Transmit 1 char in TXData (20Eh)
Transmit table (string address should be in R11)
Prepare halfduplex software UART for receive
Prepare halfduplex software UART for transmit
INT_RXTX
0FFDAh
Interrupt service routine for receive and transmit
Ret_Mon
0FFDCh
Return to the Monitor with a br Ret_Mon statement
† _{Calling TX_Char, TX_Table, TX_Prep, or RX_Prep enables the GIE flag in the status register (SR). The GIE bit remains}
set even if it was disabled before calling these routines.
5.1 Transmission Parameters of the Software UART
The transmission parameters of the MSP-STK/EVK430x320 and EVK430x330 are:
• 2400 Baud
• 1 start-bit
• 7 data-bits
• 1 parity-bit (even)
• 1 stop-bit
The RTS and DTR pins of the serial port must be set to high to provide the supply voltage for the STK/EVK
if no battery is assembled. This is done automatically in the Windows HyperTerminal program. If other
communication software is used, the specified pin levels must be met.
5.2 Identification of Bit Pattern AA55h
The interrupt service routine INT_RXTX is used for the receive and transmit function. If another INT_RXTX
service routine is being used, the identification bit pattern AA55h must be stored in memory location 3DEh
(5DEh for the MSP430x33x family). Otherwise, the INT_RXTX service routine will never branch program
execution to the vector located in the user interrupt vector table. This pattern remains in memory until it is
changed by the program or the power is switched off.
5–1