Implement ADDR instruction

[craigthomas]

Implement the ADDR 6309 instruction mnemonic in the assembler. Adds contents of a source register to the contents of the destination register. All registers except for Q and MD are allowed.

Immediate - $1030, 3 bytes

The command works with the following syntax:

ADDR r0,r1

Where r0 is the source and r1 is the destination. The source is stored as the high nibble of the operand byte, and the destination is stored as the low nibble of the operand byte. Valid source and destination values are:

0000 - D
0001 - X
0010 - Y
0011 - U
0100 - S
0101 - PC
0110 - W
0111 - V
1000 - A
1001 - B
1010 - CC
1011 - DP
1110 - E
1111 - F

Example:

$10 30 8E     ADDR A,E