qh[3..0]、ql[3..0]分别输出高位和低位的BCD码。 subdesign bcd_m60(    clk, cr, en               : input;    qh[3..0], ql[3..0], c0    : output;)variable    counth[3..0], countl[3..0]: dff; begin    counth[].clk = clk;    countl[].clk = clk;    counth[].clrn = cr;    countl[].clrn = cr;    qh[] = counth[];    ql[] = countl[];        if en then        if countl[] < 9 then            countl[] = countl[] + 1;            counth[] = counth[];            c0 = gnd;        elsif counth[] < 5 then            counth[] = counth[] + 1;            countl[] = 0;            c0 = gnd;        else             counth[] = 0;            countl[] = 0;            c0 = vcc;        end if;    else        counth[] = counth[];        countl[] = countl[];    end if; end;

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