Sd card decoder

-- Z-controller spi
zc_spi_start <= '1' when cpu_a_bus(7 downto 0)=X"57" and cpu_iorq_n='0' and cpu_m1_n='1' and loader_act='0' and is_flash_not_sd='0' else '0';
zc_wr_en <= '1' when cpu_a_bus(7 downto 0)=X"57" and cpu_iorq_n='0' and cpu_m1_n='1' and cpu_wr_n='0' and loader_act='0' and is_flash_not_sd='0' else '0';
port77_wr <= '1' when cpu_a_bus(7 downto 0)=X"77" and cpu_iorq_n='0' and cpu_m1_n='1' and cpu_wr_n='0' and loader_act='0' and is_flash_not_sd='0' else '0';

process (port77_wr, loader_act, reset, clk_bus)
    begin
        if loader_act='1' or reset='1' then
            zc_cs_n <= '1';
        elsif clk_bus'event and clk_bus='1' then
            if port77_wr='1' then
                zc_cs_n <= cpu_do_bus(1);
            end if;
        end if;
end process;

U_ZC_SPI: entity work.zc_spi     -- SD
port map(
    DI              => cpu_do_bus,
    START           => zc_spi_start,
    WR_EN           => zc_wr_en,
    CLC             => clk_bus, --clk_cpu,
    MISO            => DATA0,
    DO              => zc_do_bus,
    SCK             => zc_sclk,
    MOSI            => zc_mosi
);