M494 datasheet(4/22 Pages) STMICROELECTRONICS

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DEFINITION OF TERMS

The M494 has four conditions or states that it can

be in which are defined below. Logic LO 0V and

logic HI = 5V.

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VDD =0V. VPP =0V

VDD =5V. VPP = 25V.

Device driving display normally.

Data Handshake pin configured as RTS i/p.

Standby o/p = HI. All other functions operating

normally.

Standby

VDD =5V. VPP =0V.

Device driving display to show a single static bar

(g segment).

Data Handshake pin configured as RTS i/p. Stanby

o/p = LO.

All keyboard commands are disabled except any

program command On/Off, On/Stanby.

Memory sequence up or down, 1 * and

±10 (dec-

ade) commands.

Analog controls. Tuning, AV, MS and AFC defeat

o/p’s = LO. Band o/p’s = HI (externally pulled up).

See Standby section for more detail.

Off

VDD =5V. VPP = 0V. Device not driving display.

Data Handshake pin configured as OFF o/p.

Standby o/p = LO. Display disabled and Display

drive o/p = HI (externally pulled up).

All keyboard commands disabled except ON/OFF.

Remote and data command sources disabled.

Analog controls, Tuning, AV, MS and AFC defeat

o/p’s = HI (externally pulled up).

FUNCTIONAL DESCRIPTION (clock frequency = 500kHz)

VDD &VSS

VDD =+ 5V

± 5%. When applied, an internal power

on reset of 110ms is generated. The voltage thresh-

old for the reset is in the range 3 to 3.5V but is in

fact the point at which the internal clock phases

start.

VSS = 0V. This pin is connected to the substrate of

the i.c. and is the reference for all parameters of

the device.

Oscillator I/O

The frequency of the oscillator should be between

445 and 510kHz using a cheap ceramic resonator.

The reference frequency of the remote control

transmitter must also be in the same range i.e. if

the oscillator frequency is 455kHz then the trans-

mitter frequency could be 510kHz or vice versa.

Test

This pin is normally used for post fabrication testing

purposes only and should be tied to VSS. However

this pin can be used by SGS-THOMSON or the

OEM to enable external loading of the memory.

Details of how to achieve this can be furnished by

SGS-THOMSON.

Remote Control Input

The integrated RC receiver decodes signals trans-

mitted by the M708 (address 10). The minimum

signal amplitude should be 0.5V peak to peak at

the input pin. The minimum pulse width should be

µs.

The signal from the preamplifier (TDA8160) is

brought to the RC signal input via an AC coupling

network (see Figure 1).

VDD (TDA8160)

2.2k

Ω

4.7nF

12V

10k

Ω

4.7nF

TDA8160

M494

Figure 1

The input is self biased to approx. 1.5V. When a

large signal is applied to the input a level shift will

take place predominantly due to the coupling net-

work.

However another time constant is also visible due

to the coupling C and the internal resistor Ri. (see

Figures. 2 & 3).

Remote

Control I/P

to Cct

1.5V

Figure 2

M494

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