Examples:
call far ptr 1008:3187 ; 9A 87 31 08 10
call far [bx] ; FF 1F
Usage:
CALL FAR expects a single operand ("argument"), which can be either a direct address (1st example) or indirect address (2nd example).
Then, it takes the following actions:
1. push the value of CS to the stack
2. push the value of IP to the stack (IP already points to the *next* opcode, that is – the one after the CALL FAR opcode)
3. set the values of CS and IP to the given address
In general, if you can't find documentation for some opcode – you can try going through the engine's source code. That way you can see for yourself exactly what the opcode does.