Mullard SAA5050 teletext character generator pinout
DIP-28. Teletext character generator: turns 7-bit character codes into rounded characters, colors and block graphics.
Takes 7-bit codes latched from RAM (IC15 on the Model B), a 6 MHz dot clock on TR6 and 1 MHz on F1, and drives open-drain R, G, B outputs into the video ULA. It needs no RAM of its own; 1 KB of screen memory holds the page. Faults that appear only in MODE 7 (and 135 on the Master) are this chip, its 6 MHz clock or the latch. A cursor but no text = no 6 MHz. On the BBC: SUPERIMPOSE (pin 2) is held low, DATA and DLIM (3, 11) are tied off, BCS (15) is pulled up and Y and BLAN (21, 25) are unused; D1-D7 carry BBC data bits D0-D6; GLR (12) comes from 6845 HSYNC through an inverter and DEW (13) from 6845 VSYNC; R, G, B (24, 23, 22) go to VIDPROC RIN, GIN, BIN; TR6 (19) is made from 8 and 4 MHz (IC40/IC38 on the Model B), uneven, with no part narrower than about 40 ns (Master SM 7.3.6).
Open the interactive SAA5050 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | VSS | ground | Ground. |
| 2 | SUPERIMPOSE | io | Superimpose (open drain). |
| 3 | DATA | ctrl | Remote control data input (TV use). |
| 4 | D1 | data | Character data bit 1. |
| 5 | D2 | data | Character data bit 2. |
| 6 | D3 | data | Character data bit 3. |
| 7 | D4 | data | Character data bit 4. |
| 8 | D5 | data | Character data bit 5. |
| 9 | D6 | data | Character data bit 6. |
| 10 | D7 | data | Character data bit 7. |
| 11 | DLIM | ctrl | Remote control data clock. |
| 12 | GLR | ctrl | General line reset (line timing). |
| 13 | DEW | ctrl | Data entry window (field timing). |
| 14 | CRS | ctrl | Character rounding select (odd/even field). |
| 15 | BCS | ctrl | Big character select. |
| 16 | TLC | ctrl | Transmitted large character (double height) output. |
| 17 | NC | nc | Not connected. |
| 18 | VDD | power | +5 V. |
| 19 | TR6 | clock | 6 MHz dot clock. |
| 20 | F1 | clock | 1 MHz character clock. |
| 21 | Y | video | Monochrome video (open drain). |
| 22 | B | video | Blue video out (open drain). |
| 23 | G | video | Green video out (open drain). |
| 24 | R | video | Red video out (open drain). |
| 25 | BLAN | video | Blanking output (open drain). |
| 26 | LOSE | ctrl | Load output shift register enable (display enable, delayed). |
| 27 | PO | ctrl | Picture on input. |
| 28 | DE | ctrl | Display enable input. |
Fitted in
- BBC Micro Model B IC5
- BBC Master 128 IC32