Magic numbers

There are 2 hex numbers used in etherForth code that need explaining. These are instructions sent to a neighbor to be executed from the comm port:

120aa

The code for a call to address aa. The call instruction is in slot 0, so has a full range of addresses. The neighbor will execute the call, pushing the port address onto return. Returning from the call, execution continues from the port.

This is the value of literals like right that are used to set a port address or sometimes as a call to a port.

56aa

The code for @p call. It's similar to 120aa with @p prefixed. @p is in slot 0 and call in slot 1. An address for slot 1 can access RAM (or ROM), but can't access a port.

This is an efficient way to pass a parameter to a word. The neighbor will execute @p to fetch the next word you send, then execute the call.

Incidently, these numbers provide calibration as to what code looks like on the chip. Confusing inversion and bit alternation are performed in the PC on the way to the chip.