Introduction Serial Communications
------------------------------------------------------------------------------
 COM_BREAK()  Creates a break on a transmission line
 COM_CLOSE()  Clears the receiving buffer and closes the com port
 COM_COUNT()  Counts the number of characters in the input buffer
 COM_CRC()    Computes a Cyclic Redundancy Check (CRC) for the string
 COM_CTS()    Queries the Clear To Send (CTS) status
 COM_DCD()    Queries the Data Carrier Detect (DCD) status
 COM_DOSCON() Provides screen output through DOS--ANSI.SYS terminal emulation
 COM_DSR()    Queries the Data Set Ready (DSR) status
 COM_DTR()    Queries/sets the Data Terminal Ready (DTR) status
 COM_ERRCHR() Defines replacement for a character not received correctly
 COM_EVENT()  Designates which event at the port triggered a key trap
 COM_FLUSH()  Clears the receiving buffer
 COM_GETIO()  Determines the base address of a port
 COM_GETIRQ() Determines the interrupt request for a port
 COM_HARD()   Turns the hardware handshake (automatic CTS) on/off
 COM_INIT()   Initializes the port parameters
 COM_KEY()    Monitors the port using key traps
 COM_LSR()    Reads the Line Status Register (LSR)
 COM_MCR()    Reads or sets the Modem Control Register (MCR)
 COM_MSR()    Reads the Modem Status Register (MSR)
 COM_NUM()    Gives the number of the highest available serial interface port
 COM_OPEN()   Opens the port and initializes the buffer
 COM_READ()   Reads characters from the receiving buffer
 COM_REMOTE() Determines the clear character for the receiving buffer
 COM_RING()   Queries the ring line
 COM_RTS()    Queries or sets the Request To Send (RTS)
 COM_SCOUNT() Counts number of characters in the background sending buffer
 COM_SEND()   Transmits data directly or in the background
 COM_SETIO()  Changes the base address for a port
 COM_SETIRQ() Changes the interrupt request for a port
 COM_SFLUSH() Deletes the sending background buffer
 COM_SKEY()   Monitors port using key traps during background transmission
 COM_SMODE()  Determines the current status of a background transmission
 COM_SOFT()   Queries or sets the software handshake (automatic XON/XOFF)
 COM_SOFT_R() Tests to see if an XOFF character has been received
 COM_SOFT_S() Tests to see if buffer has automatically sent an XOFF character
 XMOBLOCK()   Generates a block for XMODEM transmission
 XMOCHECK()   Tests a received XMODEM block
 ZEROINSERT() Inserts a 0-bit after every fifth 1-bit
 ZEROREMOVE() Removes 0-bits in a file block