All the microcode I've ever written (or seen) was written in a special _assembly_ language. Or at least I'd class it as that as (a) one 'line' of microcode corresponded to one microinstruction and (b) the language statements were pretty close to the hardware definition. Here's a PERQ microinstruction : R0:=R0+R1, if neq goto(loop); The first 'phrase' defines the contents of X and Y fields (select particular registers) AMUX, BMUX fields (gate registers to ALU inputs, rather than, say gating a constant there) ALU field (do an addition operation) W field (we want to write it back to a register and not just set the flags) The second phrase sets the Condition field (to select the 'not equal' condition) Jump field (to do a got and not just a next instruction, say) SF and Z fields (to define the jump address). So the actual machine instruction is pretty close to the higher level version. OK, some fields (Z in particular) can be set by several different types of phrase, as the Z field is used for jump addresses and IO addresses and shifter control and constants and... Yes the assembler moans if you try to set it in 2 different ways in the same instruction. -tony