saa5050

Files
file	saa5050.cdl
	CDL implementation of Mullard SAA5050.

Detailed Description

Modules

module saa5050::saa5050	(	clock	clk_2MHz,
		input bit	clk_1MHz_enable,
		input bit	reset_n,
		input bit	superimpose_n,
		input bit	data_n,
		input bit	data_in[7],
		input bit	dlim,
		input bit	glr,
		input bit	dew,
		input bit	crs,
		input bit	bcs_n,
		output bit	tlc_n,
		input bit	lose,
		input bit	de,
		input bit	po,
		output bit	red[6],
		output bit	green[6],
		output bit	blue[6],
		output bit	blan,
		input t_bbc_micro_sram_request	host_sram_request
	)

This module instantiates the teletext module to provide a teletext decoder that is compatible with the SAA5050 as it is used in the BBC microcomputer (i.e. some features of the chip are not supported, such as superimpose).

Parameters

[in]	clk_2MHz	Supposedly 6MHz pixel clock (TR6), except we use 2MHz and deliver 3 pixels per tick; rising edge should be coincident with clk_1MHz edges
[in]	clk_1MHz_enable	Clock enable high for clk_2MHz when the SAA's 1MHz would normally tick
[in]	reset_n	Active low reset
[in]	superimpose_n	Not implemented
[in]	data_n	Serial data in, not implemented
[in]	data_in	Parallel character data in
[in]	dlim	Not implemented, clocks serial data in somehow
[in]	glr	General line reset, can be tied to hsync - assert once per line before data comes in
[in]	dew	Data entry window - used to determine flashing rate and resets the ROM decoders - can be tied to vsync
[in]	crs	Character rounding select - drive high on even interlace fields to enable use of rounded character data (kinda indicates 'half line')
[in]	bcs_n	Assert (low) to enable double-height characters (?)
[out]	tlc_n	Asserted (low) when double-height characters occur (?)
[in]	lose	Load output shift register enable - must be low before start of character data in a scanline, rising with (or one tick earlier?) the data; changes off falling F1, rising clk_1MHz
[in]	de	Display enable
[in]	po	Picture on
[out]	red	Red pixels out, 6 per 2MHz clock tick
[out]	green	Green pixels out, 6 per 2MHz clock tick
[out]	blue	Blue pixels out, 6 per 2MHz clock tick
[out]	blan	Not implemented
[in]	host_sram_request	Write only, writes on clk_2MHz rising, acknowledge must be handled by supermodule