TITLE "Asynchronous Transmitter"; 


%//////////////////
// INCLUDE FILES //
//////////////////%

INCLUDE "lpm_dff.inc";
INCLUDE "lpm_mux.inc";
INCLUDE "lpm_counter.inc";
INCLUDE "clk_pdiv.inc";
INCLUDE "filterx.inc";
INCLUDE "par_gen.inc";
INCLUDE "shiftreg.inc";


%/////////////////////
// INPUTS & OUTPUTS //
/////////////////////%

SUBDESIGN TX
(
 CLK, RESET, CfgReg[6..0], TxReg[7..0], DIVISOR[16..0], TxSTART	: INPUT;	-- Controller Interface
 TxEND, TxSTATUS												: OUTPUT;
 Tx																: OUTPUT;
XOUT[3..0]														: OUTPUT;
)


%//////////////////////////
// VARIABLE DECLARATIONS //
//////////////////////////%

VARIABLE

% INTERNAL VARIABLES %
 TxCLK2										: NODE;		-- Tx Baud Rate Clock x2
 TxCLK,			TxCkc						: NODE;		-- Tx Baud Rate Clock,			CLEAR-Input
 TxSR,			TxSRd[7..0], TxSRe, TxSRl	: NODE;		-- Tx Data Shift Register, 		D-Inputs, ENA-Input, LOAD-Input
 Txd										: NODE;		-- (Tx Output Flip-Flop), 		D-Input
 MPLXi[3..0], MPLXs[1..0]					: NODE;		-- (Tx Output Multiplexer), 	DATA-Inputs, SEL-Inputs
 TxCNT[4..0],	TxCNTe, TxCNTc				: NODE;		-- Transmitter Bit Counter, 	ENA-Input, ACLR-Input
 TxPar,			TxPard[7..0]				: NODE;		-- Tx Parity,					DATA-Input
 TxENA										: NODE;		-- Tx Enable Signal
 PARITY[1..0]								: NODE;		-- Parity Type
 DATABITS[1..0]								: NODE;		-- Number of Data Bits
 STOPBITS[1..0] 							: NODE;		-- Number of Stop Bits
 HANDSHAKE									: NODE;		-- Handshaking Type

% STATE MACHINES %
 Txss	: MACHINE WITH STATES (Tx0, Tx1, Tx2, Tx3, Tx4, Tx5, Tx6, Tx7, Tx8);	-- Transmitter


%//////////////////
// LOGIC SECTION //
//////////////////%

BEGIN

% DEFAULT VALUES %
 DEFAULTS
  TxCkc=GND;
  TxSRe=GND; TxSRl=GND;
  TxCNTe=GND; TxCNTc=GND;
  TxEND=GND;
 END DEFAULTS;

% IN-LINE ASSIGNMENTS %
 TxCLK2		= Clk_PDiv (CLK, DIVISOR[],, RESET # TxCkc)					-- Tx Baud Clock x2
              WITH (WIDTH=17)
              RETURNS (.out);
 TxCLK		= LPM_DFF (!TxCLK, TxCLK2,,,,,,, RESET # TxCkc,,)			-- Tx Baud Clock
              WITH (LPM_WIDTH=1)
              RETURNS (.q[]);
 Tx			= LPM_DFF (Txd, TxCLK,,,,,,,, RESET # Tx0,)					-- Tx Output Flip-Flop
              WITH (LPM_WIDTH=1)
              RETURNS (.q[]);

 TxSR		= ShiftReg (TxCLK, TxSRd[], RESET, TxSRl, TxSRe, GND)		-- Tx Output Shift Register
              WITH (WIDTH=8, MSB_FIRST="NO", SHIFT_MODE="ON")
              RETURNS (.dout);
 Txd		= LPM_MUX (MPLXi[3..0], MPLXs[1..0],,,)						-- Tx Output Multiplexer
              WITH (LPM_WIDTH=1, LPM_SIZE=4, LPM_WIDTHS=2)
              RETURNS (.result[]);
 TxCNT[]	= LPM_COUNTER (.CLOCK = TxCLK2,.CNT_EN = TxCNTe, .ACLR = RESET # TxCNTc)	-- Tx Bit Counter
              WITH (LPM_WIDTH=5, LPM_DIRECTION="UP")
              RETURNS (.q[]);
 TxPar		= Par_Gen (TxPard[7..0])									-- Tx Parity Generator
              WITH (WIDTH=8)
              RETURNS (.odd/even);
 TxENA		= LPM_DFF (VCC, CLK, GND,,,,,, RESET # Tx1, TxStart,)		-- Tx Enable Signal
              WITH (LPM_WIDTH=1)
              RETURNS (.q[]);
 TxSTATUS	= LPM_DFF (VCC, CLK, TxEND,,,,,, RESET # TxStart,,)			-- Tx Data Transmitted Flag
              WITH (LPM_WIDTH=1)
              RETURNS (.q[]);

% COMBINATORIAL LOGIC %
 PARITY[]=CfgReg[1..0];			-- UART Control Bits
 STOPBITS[]=CfgReg[3..2];
 DATABITS[]=CfgReg[5..4];
 HANDSHAKE=CfgReg[6];

 IF (DATABITS[]==0) THEN TxPard[7..5]=0; TxPard[4..0]=TxReg[4..0]; END IF;	-- Ignore High Bits in Parity Generator
 IF (DATABITS[]==1) THEN TxPard[7..6]=0; TxPard[5..0]=TxReg[5..0]; END IF;
 IF (DATABITS[]==2) THEN TxPard[7]=GND;  TxPard[6..0]=TxReg[6..0]; END IF;
 IF (DATABITS[]==3) THEN                 TxPard[7..0]=TxReg[7..0]; END IF;

 MPLXi[0]=VCC;			-- Assign Multiplexer Inputs
 MPLXi[1]=GND;
 MPLXi[2]=PARITY[1] !$ TxPar;
 MPLXi[3]=TxSR;

 Txss.CLK	= CLK;		-- Tx State Machine Clock and Reset
 Txss.RESET	= RESET;

% TRANSMITTER STATE MACHINE %
 CASE Txss IS

  WHEN Tx0 =>
   MPLXs[]=0;													-- Select VCC
   TxCkc=VCC;													-- Clear Tx Clock
   TxCNTc=VCC;													-- Clear Tx Bit Counter
   TxSRl=VCC;													-- Enable Load of Tx Shift Register
   TxSRd[7..0]=TxReg[7..0];										-- Setup Data Load for Tx Shift Register
	XOUT[] = 0;
   IF (TxENA & !HANDSHAKE) THEN 								--((HANDSHAKE & CTSf & DSRf) # !HANDSHAKE)) THEN	-- Wait until New Tx Data and CTS/DSR
    Txss=Tx1;
   ELSE Txss=Tx0; END IF;

  WHEN Tx1 =>	-- Clear Tx Enable Signal
   Txss=Tx2;
	XOUT[] = 1;

  WHEN Tx2 =>
   MPLXs[]=1;											-- Select GND
   TxCNTe=VCC;											-- Enable Tx Bit Counter
	XOUT[] = 2;
   IF (TxCNT[]==2) THEN Txss=Tx3;						-- Wait until Start Bit shifted out
   ELSE Txss=Tx2; END IF;

  WHEN Tx3 =>
   MPLXs[]=3;											-- Select Data
   TxSRe=VCC;											-- Shift out Data
   TxCNTe=VCC;											-- Enable Tx Bit Counter
	XOUT[] = 3;
   IF ((DATABITS[]==0 & TxCNT[]==12)
     # (DATABITS[]==1 & TxCNT[]==14)
     # (DATABITS[]==2 & TxCNT[]==16)
     # (DATABITS[]==3 & TxCNT[]==18)) THEN Txss=Tx4;	-- Wait until all Data Bits Shifted out
   ELSE Txss=Tx3; END IF;

  WHEN Tx4 =>
   TxCNTc=VCC;											-- Clear Tx Bit Counter
	XOUT[] = 4;
   IF (PARITY[]==0 # PARITY[]==3) THEN Txss=Tx7;		-- Check if Parity Enabled
   ELSE Txss=Tx5; END IF;

  WHEN Tx5 =>
   MPLXs[]=2;											-- Select TxPar
   TxCNTe=VCC;											-- Enable Tx Bit Counter
	XOUT[] = 5;
   IF (TxCNT[]==2) THEN Txss=Tx6;						-- Wait until Parity Bit Shifted out
   ELSE Txss=Tx5; END IF;

  WHEN Tx6 =>
   TxCNTc=VCC;		-- Clear Tx Bit Counter
   Txss=Tx7;
	XOUT[] = 6;

  WHEN Tx7 =>
   MPLXs[]=0;														-- Select VCC
   TxCNTe=VCC;														-- Enable Tx Bit Counter
   IF ((STOPBITS[]==0 # STOPBITS[]==3) & TxCNT[]==2) THEN Txss=Tx8;	-- Wait until Stop Bit 1 Shifted out
   ELSIF (STOPBITS[]==1 & TxCNT[]==3) THEN Txss=Tx8;				-- Wait until Stop Bit 1.5 Shifted out
   ELSIF (STOPBITS[]==2 & TxCNT[]==4) THEN Txss=Tx8;				-- Wait until Stop Bit 2 Shifted out
   ELSE Txss=Tx7; 
   END IF;
	XOUT[] = 7;


  WHEN Tx8 =>
   TxCkc=VCC;		-- Clear Tx Clock
   TxEND=VCC;		-- Set Tx End Flag
   Txss=Tx0;
	XOUT[] = 8;

 END CASE;

END;