M494 datasheet(12/22 Pages) STMICROELECTRONICS

12 / 22 page

FUNCTIONAL DESCRIPTION (continued)

Audio Visual Outputs

Two audio visual outputs are provided for automat-

ic selection of a VCR and/or personal computer.

The logic state of the pins depends on the AV option

selected, the program option and the program

number selected according to the truth tables be-

low :

Table 3 : AV Option 1 (16/20 Programs)

Program

AV0

AV1

16/0

15/19

Others

Table 4 : AV Option 2 (16/20 Programs)

Program

AV0

AV1

8/8

7/7

6/6

Others

External pull up resistors must be used to realise a

logic HI as the outputs are open drain transistors.

See I/O Configuration.

AFC Defeat Output

The AFC defeat output is a TTL compatible signal

that is capable of switching the AFC circuitry in and

out. The AFC defeat output is pulled LO on any

program change including memory sequence up

and down and is held LO for 500ms after execution

of the command. When tune up or down are com-

manded the AFC defeat output is taken to logic LO.

After the tuning operation the AFC defeat is held

LO for 1 second after the key is released (see

Figure 9). On power on & start up resets it is taken

to logic LO for approx. 1.1 seconds.

AFC DEFE AT

OUTPUT

TUNE UP/DO WN :

KEYED

RELEASED

Figure 9

Standby

The standby output is a push pull output capable

of directly driving an NPN transistor for switching

a relay. The states of this pin are defined in the

definition of terms. When standby is commanded,

available from all command sources as Standby or

On/Standby commands, the standby output is en-

abled.

If the device goes into Standby from On then any

program command will bring the device On with

that program selected. On/Off command from key-

boar d o nl y w il l exe cute the Off funct io n.

On/Standby, Memory sequence up or down, 1 *

and

± 10 (decade) commands from any command

source will bring the device On in the program

selected before Standby with the display showing

that program only, i.e. the device executes an On

command only.

If the device goes into Standby from Powered down

then the On/Off command from keyboard only and

any program command, On/Standby, Memory se-

quence up or down, 1 * and

± 10 (decade) com-

mands from any command source will bring the

device On in program 1. i.e. the device executes

an On command only.

Option Select

The Option select pin provides an extra line that

performs a ”hard wired keyboard function” in con-

junction with the keyboard scanning lines D0-D4.

This line has integrated logic associated with it

that enables one or many of the functions to be

active simultaneously. In contrast, the keyboard

inputs a-g will allow one key active at any given

time. See keyboard section.

Various options can be selected by the connection

or not of a diode as shown in Figures 7 & 8.

From left to right along the Option select line col-

umn 1 selects the number of programs. A diode

connected here selects 20 programs (full comple-

ment) and no diode (default) selects 16 programs

only that can be accessed. The 20 program option

only enables selection of 1 * or decade modes in

column 4. In column 2 the AV option defines the

state of the AV outputs for two protocols.

These are described in section Audio visual output.

Column 3 defines the state the M494 powers up in.

If no connection of a diode (default) is made here

the device powers up in the Off state. If a diode is

present then the device powers up in the Standby

state. In column 4, activated by the 20 program

option only, the presence of a diode places the

device in 1 * mode and the absence of a diode

selects decade mode. The diode and switch in

column 5 defeats the skip condition and enables

program memory words to be read with the skip

flag set.

This allows programming (or reprogramming) of

previously skipped words.

M494

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