Digilent Parallel Interface Model - Manual (Page 7)

Digilent Parallel Interface Model Digilent, Inc.
www.digilentinc.com Copyright Digilent, Inc. Page 7
signal ctlEppAstb : std_logic;
signal ctlEppDstb : std_logic;
signal ctlEppDir : std_logic;
signal ctlEppWr : std_logic;
signal ctlEppAwr : std_logic;
signal ctlEppDwr : std_logic;
signal busEppOut : std_logic_vector(7 downto 0);
signal busEppIn : std_logic_vector(7 downto 0);
signal busEppData : std_logic_vector(7 downto 0);
-- Registers
signal regEppAdr : std_logic_vector(3 downto 0);
signal regData0 : std_logic_vector(7 downto 0);
signal regData1 : std_logic_vector(7 downto 0);
signal regData2 : std_logic_vector(7 downto 0);
signal regData3 : std_logic_vector(7 downto 0);
signal regData4 : std_logic_vector(7 downto 0);
signal regData5 : std_logic_vector(7 downto 0);
signal regData6 : std_logic_vector(7 downto 0);
signal regData7 : std_logic_vector(7 downto 0);
signal regLed : std_logic_vector(7 downto 0);
signal cntr : std_logic_vector(23 downto 0);
------------------------------------------------------------------------
-- Module Implementation
------------------------------------------------------------------------
begin
------------------------------------------------------------------------
-- Map basic status and control signals
------------------------------------------------------------------------
clkMain <= mclk;
ctlEppAstb <= astb;
ctlEppDstb <= dstb;
ctlEppWr <= pwr;
pwait <= ctlEppWait; -- drive WAIT from state machine output
-- Data bus direction control. The internal input data bus always
-- gets the port data bus. The port data bus drives the internal
-- output data bus onto the pins when the interface says we are doing
-- a read cycle and we are in one of the read cycles states in the
-- state machine.
busEppIn <= pdb;
pdb <= busEppOut when ctlEppWr = '1' and ctlEppDir = '1' else "ZZZZZZZZ";
-- Select either address or data onto the internal output data bus.
busEppOut <= "0000" & regEppAdr when ctlEppAstb = '0' else busEppData;
rgLed <= regLed;
ldg <= '1';
-- Decode the address register and select the appropriate data register
busEppData <= regData0 when regEppAdr = "0000" else
regData1 when regEppAdr = "0001" else
regData2 when regEppAdr = "0010" else