IOP16 ANSI Display

Multicomp FPGA (VHDL Template) VGA

Interface mimics ACIA software interface address/control/status contents

• ACIA datasheet

Programming Interface

• Two addresses, Control/status and data access

Status Register

• Register Select = 0
• Read/Write = Read
  • d0 = RDRF = Receive Data Register Full (1 = data is ready to read)
  • d1 = TDRE = Transmit Data Register Empty (1 = transmit is ready to send out data)
  • d2 = DCD = Data Carrier Detect (0 = carrier present - hardwired)
  • d3 = CTS = Clear to Send (0 = Clear to Send - ready to accept data - hardwired)
  • d7 = IRQ = Interrupt Request (1 = Interrupt present)

Control Register

• Register Select = 0
• Read/Write = Write
  • d1,d0 = Control (11 = Master Reset)
  • d6,d5 = TC = Transmitter Control (RTS = Transmitter Interrupt Enable/Disable)
  • d7 = Interrupt Enable (1=enable interrupts)

Data Register

• Register Select = 1
  • Read = Read data from the data register (not implemented due to kbd removal)
  • Write = Write data to the data register

ANSI ESC Codes

Example Code

Initialize the VDU

• Destroys Reg0

INITVDU	LRI	0X00	0X03	RESET TERMINAL COMMAND
	IOW	0X00	0X0A	WRITE VDU CMD REG
	LRI	0X00	0X20	TX CTRLS RTS
	IOW	0X00	0X0A	WRITE VDU CMD REG
	RTS			

Clear Screen, set to yellow characters

• Destroys Reg1

CLRSCR	LRI	0X01	0X0C	ANSI CLEAR THE SCREEN CMD
	JSR	WRVDU		WRITE OUT CHAR IN R1
YELLOW	LRI	0X01	0X1B	ESC SEQ FOR YELLOW CHARS
	JSR	WRVDU		WRITE OUT CHAR IN R1
	LRI	0X01	0X5B	[
	JSR	WRVDU		WRITE OUT CHAR IN R1
	LRI	0X01	0X33	3
	JSR	WRVDU		WRITE OUT CHAR IN R1
	LRI	0X01	0X33	3
	JSR	WRVDU		WRITE OUT CHAR IN R1
	LRI	0X01	0X6D	m 
	JSR	WRVDU		WRITE OUT CHAR IN R1
	RTS			

Write char to the VDU

• Pass char in Reg1
• Destroys Reg0

WRVDU		JSR	WTVDUTXRDY		WAIT VDU TX READY
		IOW	0X01		0X0B	WRITE OUT R1 TO SCREEN
		RTS			
WTVDUTXRDY	IOR	0X00		0X0A	READ VDU STATUS
		ARI	0X00		0X02	TX EMPTY FLAG
		BEZ	WTVDUTXRDY		WAIT UNTIL TX EMPTY
		RTS			

Write CR-LF to the screen

• Destroys Reg1

VDUCRLF	LRI	0X01	0X0D	CR
	JSR	WRVDU		
	LRI	0X01	0X0A	LF
	JSR	WRVDU		
	RTS			

Write String to the screen

• Requires IOP16 Constants Unit
• Pass start address of string in Reg1
  • Assembler autogenerates table and start addresses
  • Strings are NULL terminated
• Destroys Reg1

PRSTRLF	IOW	0X00	0X0E	LOAD CONSTANTS ADDRESS
PRSTR2	IOR	0X01	0X0E	READ CHAR (NEXT)
	CMP	0X01	0X00	IS END OF STRING?
	BNE	SKIPPS		NOT END OF STRING
	LRI	0X01	0X0D	CR
	JSR	WRVDU		
	LRI	0X01	0X0A	LF
	JSR	WRVDU		
	RTS			RETURN IF END
SKIPPS	JSR	WRVDU		PRINT TO VDU
	JMP	PRSTR2		LOOP UNTIL NULL TERM

VHDL Code

Entity

-- ____________________________________________________________________________________
-- Grant Searle's VGA driver from Multicomp
-- DGG removed the PS/2 keyboard, Composite output and CTS
-- Interface matches ACIA software interface address/control/status contents

vdu : entity work.ANSIDisplayVGA
  GENERIC map (
    EXTENDED_CHARSET    => 0, -- 1 = 256 chars
                              -- 0 = 128 chars
    COLOUR_ATTS_ENABLED => 0, -- 1 = Color for each character
                              -- 0 = Color applied to whole display
    SANS_SERIF_FONT     => 1  -- 0 => use conventional CGA font
                              -- 1 => use san serif font
)
  port map (
    clk     => i_clk,
    n_reset => w_resetClean_n,
    -- CPU interface
    n_WR    => not W_VDUWr,
    n_rd    => not W_VDURd,
    regSel  => w_periphAdr(0),
    dataIn  => w_periphOut,
    dataOut => w_VDUDataOut,
    -- VGA video signals
    hSync   => hSync,
    vSync   => vSync,
    videoR0 => videoR0,
    videoR1 => videoR1,
    videoG0 => videoG0,
    videoG1 => videoG1,
    videoB0 => videoB0,
    videoB1 => videoB1
);

Signals

-- Decodes/Strobes
...
  signal W_VDUWr       : std_logic;
  signal W_VDURd       : std_logic;

-- Interfaces
...
  signal w_VDUDataOut  :  std_logic_vector(7 downto 0);

Hook-up code

-- Strobes/Selects
...
w_VDUWr <= '1' when ((w_periphAdr(7 downto 1) = "0000101") and (w_periphWr= '1')) else '0';
w_VDURd <= '1' when ((w_periphAdr(7 downto 1) = "0000101") and (w_periphRd = '1')) else '0';

-- Peripheral bus read mux
w_periphIn <=	...
  w_VDUDataOut			when w_periphAdr(7 downto 1) = "0000101"	else
...

Resources (10CL006)

• Logic Cells: 918
• Registers: 203
• Memory Bits: 24576 (128 chars)
• M9Ks: 3 (128 chars)
• Memory Bits: 32768 (256 chars)
• M9Ks: 4 (256 chars)
• Resource usage can be reduced by changing the generics below
  • EXTENDED_CHARSET=0, COLOUR_ATTS_ENABLED=0 - Uses 3 M9K blocks
  • EXTENDED_CHARSET=1, COLOUR_ATTS_ENABLED=0 - Uses 4 M9K blocks
  • EXTENDED_CHARSET=0, COLOUR_ATTS_ENABLED=1 - Uses 5 M9K blocks
  • EXTENDED_CHARSET=1, COLOUR_ATTS_ENABLED=1 - Uses 6 M9K blocks