VBA Serial Port Functions

send, receive, check and wait for data

First parameter (1) is a valid¹ and started COM Port number on host PC.

VBA Function	TS	Description
`check_com_port(1)`	No	Returns number of input characters waiting to be read (no wait). Return value -1 indicates error.
`wait_com_port(1)`	Yes	Wait for up to 333mS (default) before timing out. Returns `True` if receive data waiting.
`wait_com_port(1,500)`	Yes	As above, specify maximum wait time (500) in milliseconds.
`get_com_port(1)`	No	Receives a single-character string.
`put_com_port(1,"A")`	No	Sends a single-character string.
`read_com_port(1)`	No	Reads an unspecified number ² of waiting characters.
`read_com_port(1,20)`	No	Reads up to specified number ² (20) of waiting characters.
`send_com_port(1,V)`	Yes	Sends variable V. Function converts V to string and calls `transmit_com_port`. ³
`send_com_port(1,$B$5)`	Yes	Sends contents of Cell $B$5 ⁴ to com port (Excel Worksheet Only)
`receive_com_port(1)`	Yes	Receives all data from port ³⁵
`transmit_com_port(1,"QWERTY")`	Yes	Sends supplied string QWERTY to port ³
`transmit_com_port(1,COMMANDS)`	Yes	Sends supplied string constant or variable COMMANDS to port ³

Functions shown as TS=No return within a few milliseconds.
Functions shown as TS=Yes are timesliced to avoid VBA hanging with a 'not responding' message.

Valid Minimum and Maximum port numbers should be defined in declarations section at the start of the module. ↩
Maximum number of waiting characters read is approximately = (baud rate / 10) ↩ ↩²
Function can block for extended periods with VBA remaining responsive before returning. ↩ ↩² ↩³ ↩⁴
Excel will re-send if Cell $B$5 value changes ↩
Function includes read wait and exit timers and returns when exit timer expires. ↩