Serial communications: Port selection

In dialect 29 we introduced the ability to use more than one serial communications port. Here's how it works:

• Serial ports are addressed in the range 251 to 255. These are addresses in the RAM address space that do not actually have RAM "behind them".
• The "default" port is the controller's programming port. It sits at address 251.
• There is a whole collection of instructions for manipulating the default port at 251. A typical one of these is ComRx_fGetNum, which retrieves a floating point number from the serial input buffer. Historically these are the original instructions.
• There is a second set of instructions for accessing any other serial ports that may exist in a given controller. These all start with an 'a', for example aComRx_fGetNum.
• Most of the ComRx... and aComRx... instructions are about receiving serial data. The ones for transmitting data are those like iifPrintWFW.

When using Hash commands

When using hash commands that reference serial ports (including a USB port that is mapped as a serial port, as on the EC1), it becomes much simpler. Select the serial port using the Port hash function.