SAA5050 Series Teletext character generators

Data Sheet

Converted to HTML from SAA5050 Mullard Teletext Character Generator data sheet (Zipped TIF).

Font ROM defines 5x9 pixels in a 6x10 character cell.
There are 40 characters per line, and 25 character rows.
Thus display area is 240x250 pixels.

SAA5050 Series

Teletext character generators

The SAA5050 series of MOS N-channel integrated circuits provides the video drive signals to the television receiver necessary to produce the teletext / viewdata display. The variants are described in the Quick Reference Data and full details of the characters sets are given in Figs. 11 to 18.

Figure 1. Block diagram

PACKAGE OUTLINE
28-lead DIL; plastic (SOT-117)
Mullard July 1982

Figure 2. Pinning diagram

Quick reference data

Description

The SAA5050 is a 28 pin device which incorporates a fast access character generator ROM (4.3 k bits), the logic decoding for all the teletext control characters and decoding for some of the remote control functions. The circuit generates 96 alphanumeric and 64 graphic characters. In addition there are 32 control characters which determine the nature of the display. The SAA5050 is suitable for direct connection to the SAA5010, SAA5012, SAA5020 and SAA5040 Series integrated circuits.

The basic input to the SAA5050 is the character data from the teletext page memory. This is a 7 bit code. Each character code defines a dot matrix pattern. The character period is 1 us and the character dot rate is 6 MHz. The timings are derived from the two external input clocks F1 (1 MHz) and TR6 (6 MHz) which are amplified and re-synchronised internally. Each character rectangle is 6 dots wide by 10 TV lines high. One dot space is left between adjacent characters, and there is one line space left between rows.

Alphanumeric characters are generated on a 5 x 9 matrix, allowing space for descending characters. Each of the 64 graphic characters is decoded to form a 2 x 3 block arrangement which occupies the complete 6 x 10 dot matrix (Fig.9). Graphics characters may be either contiguous or separated (Fig.10). The alphanumeric characters are character rounded, i.e. a half dot is inserted before or after a whole dot in the presence of a diagonal in a character matrix.

The character video output signals comprise a monochrome signal and RGB signals for a colour receiver. A blanking output signal is provided to blank out the television video signal under the control of the PO and DE inputs and the box control characters (see Table 3).

The monochrome data signal can be used to inlay characters into the television video. The use of the 32 control characters provides information on the nature of the display, e.g. colour. These are also used to provide other facilities such as 'concealed display' and flashing words etc. The full character set is given in Table 1.

Handling

Inputs and outputs are protected against electrostatic charge in normal handling. However, to be totally safe, it is desirable to take normal precautions appropriate to handling MOS devices (See 'Handling MOS Devices’).

Ratings

Limiting values in accordance with the Absolute Maximum System, (IEC134)

Characteristics

Limiting values in accordance with the Absolute Maximum System, (IEC134)

Timing characteristics

For typical display of 40 characters per line. Line period = 64 µs. Field period = 20 ms.

* Taken as falling edge of 'line sync' pulse.

Notes

1. Fall time, t_f and delta t_f, are defined as shown and are measured using the circuit shown below:
   tf is measured between the 9 V and 1 V levels.
   Dt_f is the maximum time difference between outputs.
   
2. Recommended pull-up resistor for !SI is 18k.
3. The R, G, B, Y and blanking outputs are protected against short circuit to supply rails.
4. There is no maximum DLIM cycle time, provided the DLIM duty cycle is such that the t_CL max requirement is not exceeded.

Figure 3.

Special features

Flash oscillator

The circuit generates a 0.75 Hz signal with a 3:1 ON/OFF ratio to provide the flashing character facility.

Power-on-reset

When the supply voltage is switched on, the character generator will reset to TV, conceal, and not superimpose modes.

Character rounding

The character rounding function is different for the small and double height characters. In both cases the ROM is accessed twice during the character period of 1 µs. The dot information of two rows is then compared to detect the presence of any diagonal in the character matrix and to determine the positioning of the character rounding half dots.

For small characters rounding is always referenced in the same direction (i.e. row before in even fields and row after in odd fields as determined by the CRS signal).

For double height characters rounding is always referenced alternately up and down changing every line using an internally generated signal. (The CRS signal is '0' for the odd field and '1' for the even field of an interlaced tv picture).

Graphics decoder

The 64 graphics characters are decoded directly from the character data inputs and they appear on a 2 x 3 matrix. Figure 9 gives details of the graphics decoding.

Application data

The function is quoted against the corresponding pin numbers

Figure 4. Character data timing (for typical 40 character display)

Figure 5. Display period timing (for typical 40 character display)

Figure 6. Line rate clock (for line period of 64 µs)

Figure 7. Field rate clocks (for field period of 20 ms, 312.5 lines per field)

Figure 8. Remote control input timing

Figure. 9 Graphics character

Each cell is illuminated if particular 'bit' (b1, b2, b3, b4, b5, or b7) is a '1'. For graphics characters by is always a '1' – See Table 1.

Figure. 10 Character format

FIG 8. EXAMPLES OF ALPHANUMERIC AND GRAPHIC DISPLAYS

Table 1. Character data input decoding

b7..5

000

001

010

011

100

101

110

111

b4..1

0

1

2

2a

3

3a

4

5

6

6a

7

7a

<- Col

0000

0

NUL(1)

DLE(1)

0

@

P

p

0001

1

Alpha Red

Graphics Red

!

1

A

Q

a

q

0010

2

Alpha Green

Graphics Green

"

2

B

R

b

r

0011

3

Alpha Yellow

Graphics Yellow

£

3

C

S

c

s

0100

4

Alpha Blue

Graphics Blue

$

4

D

T

d

t

0101

5

Alpha Magenta

Graphics Magenta

%

5

E

U

e

u

0110

6

Alpha Cyan

Graphics Cyan

&

6

F

V

f

v

0111

7

Alpha White (2)

Graphics White (2)

'

7

G

W

g

w

1000

8

Flash

Conceal display

(

8

H

X

h

x

1001

9

Steady (2)

Contiguous Gfx (2)

)

9

I

Y

i

y

1010

10

End Box (2)

Separated Gfx

*

:

J

Z

j

z

1011

11

Start Box

ESC (1)

+

;

K

k

¼

1100

12

Normal height (2)

Black Background (2)

,

<

L

½

l

||

1101

13

Double height

New Background

-

=

M

m

¾

1110

14

S0

Hold Graphics

.

>

N

n

÷

1111

15

S1

Release Graphics (2)

/

?

O

#

o

block

Row

Control characters shown in columns 0 and 1 are normally displayed as spaces.
The SAA5050 character set is shown as example. Details of character sets are given in Figs. 11 to 18.

Table 2. Remote control command codes used in the SAA5050

x = Don't care.

Notes

1. When the power is applied the SAA5050 is set into the 'tv' mode and reset out of Superimpose and Reveal modes.
2. 'Text' mode is selected when !Sl (pin 2) is held LOW
3. Reveal mode allows display of text previously concealed by 'conceal display' control characters.
4. This code is sent from the SAA5010 or the SAA5012 Series as a repeated command. Thus Reveal mode is set for as long as the Reveal key is depressed. The SAA5050 reverts to normal 'not Reveal' mode 160 ms after the last Reveal command.
5. The Superimpose output is LOW only if Superimpose mode is set and the DE (display enable) input is HIGH.
6. The above table shows code required for functions specified. The SAA5010 or the SAA5012 Series transmits and the SAA5050 requires the inverse of these codes i.e. !b7 to !b1. The code is transmitted serially in the following order: !b7 !b1 !b2 !b3 !b4 !b5 !b6
   For full details of remote control data coding see the SAA5010 or the SAA5012 data sheets.

Table 3. Conditions affecting display (see note 3)

Notes

1. For TV mode (Picture On = '1', Superimpose mode not allowed) rows (a), (d) and (g) of Table 3 refer to display row 0 only. For all other rows text display is disabled and Blanking = '0'
2. The R, G, B outputs may contain character and background colour information. The only exception is that background colours are inhibited when Blanking = '0'
3. Valid during display period only (see Fig.5) otherwise no character or background information is displayed as blanking is determined by the Picture On. (No blanking if PO = '1').

Figure. 11 SAA5050 character set (English)