The 8088/8086 assembler in Pygmy is a regular Forth postfix assembler. For examples of how it is used, browse through PYGMY.SCR. Begin a code word with CODE and end it with END-CODE. e.g. CODE TST1 BX PUSH, NXT, END-CODE Except in special cases (& then you know what you are doing) code words must perform next somehow. In Pygmy, this code is laid down in-line by the word NXT, rather than by a jump to a central next routine. If your routine disturbs CS, DS, BP, SP, SI, DI, or BX it must restore it. The direction flag must be left clear. BP points to the return stack and SP points to the data stack. The top (data) stack item is kept in BX rather than on the actual stack. See example on previous page; it is the code for DUP. DI is dedicated to holding a zero. If you use it for any other purpose, zero it before doing NXT, DS:SI is Forth's IP register. AX is Forth's W register, but you may use it freely without restoring it. The assembler words generally end in a comma, signalling thatthey are actively comma'ing data into the dictionary. This is useful for another purpose: as the assembler words and the regular Forth words all sit in the same vocabulary (FORTH), the comma helps distinguish between similar words, e.g. THEN & THEN, It is a "structured" assembler with <set-codes> <condition> IF, XXXXXX ELSE, XXXXXX THEN, and XX #, CX MOV, BEGIN, XXXXX LOOP, etc If it is not clear from the instr whether the operand is a byte or a word, a byte is assumed. E.g. 0 [BX] PUSH, would push only a single byte. To override this, use W-PTR e.g. 0 [BX] W-PTR PUSH, For the shifts & rotates, if an immediate operand precedes it, it shifts a single bit ( e.g. 1 #, AX SHR, or even 300 #, AX SHR, for that matter). If you want it to shift based on the contents of CL, omit the immediate operand ( e.g. 4 #, CX MOV, AX SHR, ) examples to shift right 1 bit: 1 #, SI SHR, 1 #, W-PTR 17 [BX] SHR, 1 #, AL SHR, examples to shift right the # of bits in CL SI SHR, AL SHR, 1300 ) SHR, 3752 W-PTR ) SHR, IN, & OUT, (reading & writing I/O ports) use port #, AL IN, or port #, AX IN, for 8 bit ports or AL IN, or AX IN, for port in the DX register do not use AL DX IN, - the DX is implied JMP, & CALL, Long JMPs & CALLs are "not supported at this time." The instruction that does a bit by bit complement is called NOT bye Intel, but this assembler it is called COM, This assembler uses NOT, to invert the test at the beginning of an IF, e.g. CS, IF, ( do if carry set) THEN, or CS, NOT, IF, ( do if carry not set) THEN,
