register file

hey guys, I'm almost finishing up my processor but I'm a bit stuck on the register file; below is the description of what it is supposed to do:

Code:

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Build a register file that contains 8 8-bit registers. Has inputs and outputs as defined below.
        Name        Width        Input/Output
        a_sel        3        I        selects the register whose contents are to be placed on A
        b_sel        3        I        selects the register whose contents are to be placed on B
        r0_w        1        I        stores the value on RES into reg 0
        r1_w        1        I        stores the value on RES into reg 1
        r2_w        1        I        stores the value on RES into reg 2
        r3_w        1        I        stores the value on RES into reg 3
        r4_w        1        I        stores the value on RES into reg 4
        r5_w        1        I        stores the value on RES into reg 5
        r6_w        1        I        stores the value on RES into reg 6
        r7_w        1        I        stores the value on RES into reg 7
        RES        8        I        input RES bus

        A        8        O        output A bus
        B        8        O        output B bus

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BTW I'm usingl VHDL or Assembly, I'm just building this on the "gate and wire" level using tkgate.

So far I've build all 8 8bit registers. Then I build two 8 to 1 multiplexers that take all the wires from the registers (meaning 64bits go into the MUX). I send a_sel to one of the MUXes and b_sel to the other. The problem is that when in the MUX I'm ANDing a 3 bit wire (select) with an 8 bit wire it gives me a bunch of errors....any ideas?

thanks