Details, datasheet, quote on part number: MA552
CompanyZarlink Semiconductor
DatasheetDownload MA552 datasheet


Features, Applications

The is a CMOS Bilingual (ie Loop Disconnect and Multi-frequency) dialler chip with a 21. digit Last Number Redial facility. The chip can be operated in either LD mode, MF mode or a third mode in which dialling can be switched from LD to DTMF from the keypad during a call. This third mode is intended for users connected to an exchange accepting only LD signalling but may require access to facilities such as home banking and databases accepting DTMF signalling. Low power CMOS design allows the LNR store contents to be maintained by a minimal current whilst the telephone is onhook. A selectable facility allows access pauses to be recognised during manual dialling and to regenerate these pauses automatically when using the LNR facility. In order to cater for the telephone specifications of many countries and different circuit configurations the MA552 offers a variety of pin selectable and metal mask programmable options. Other features include a temperature compensated voltage reference for accurate DTMF levels independent of supply voltage and a `single pin' oscillator circuit requiring only an inexpensive external 560kHz ceramic resonator. Both Timed Break Recall (Flash) and Earth Loop Recall are supported and offer identical operating protocols.


s Selectable Loop-Disconnect or DTMF Modes s Keypad Switchable LD to DTMF s DTMF output Levels Independent of Temperature and Voltage s 21 Digit Last N~nber Redial s Automatic Pause Detection for LNR s Selectable Make/Break Ratios 2:1 and 3:2 s Uses Inexpensive 560kHz Ceramic Resonator s Banery-less Operation - Low Power CMOS s Mask Programmable Options to suit Application s PIN (Personal Identification Number) Confidentiality s Timed Break Recall (Flash) and Earth Recall


Positive supply Negative supply LD/DTMF selection and B/M ratio programming Pause and Pause Duration Selection Oscillator connection. Connect 560kHz resonator from this pin to VSS Hookswitch. A logic '1' voltage at this pin is used to indicate 'off-hook' Output to disable speech circuit during LD dialling and Recall (Flash): Note 1 'Loop-Disconnect' dialling output Unfiltered, dual tone output Unity gain amplifier output for 2-pole filter Unity gain amplifier input for 2-pole filter Output active during keying and tone transmission: Note 2

1. MASK may be used to disconnect the whole speech circuit in order to maintain the break condition whilst on-hook and during a TBR (Timed Flash) operation. 2. MUTE is provided to disable the microphone while maintaining the loop condition during DTMF transmission.

POWER-ON When power is applied to the chip, a power-on reset circuit operates and ensures that the last number redial store is cleared and all logic is reset The power-on reset circuit is designed such that if the chip supply voltage drops to a level at which the LNR store may be corrupted it will always, under all conditions, clear the store when power is restored. so that corrupt data is not retained HOOKSWITCH OPERATION The HSW input is used to inform the MA552 of whether the telephone on or off hook. Logic `0' is recognised as on-hook, Logic `1` is recognised as off-hook. When the HSW input rises from to `1` the off-hook state is recognised immediately and keypad inputs are accepted. However, when the HSW input falls from to `0' the onhook state is not recognised for 200300ms. This is so that short line breaks of less than 200ms, such as line reversals applied bv the exchange, are ignored In this case the IMP and MASK outputs will go low immediately the HSW input goes low In order to preserve current, but will resume normal operation immediately HSW goes high. ON-HOOK STATE In the on-hook state all chip outputs are set low, the oscillator circuit is inhibited and no key inputs are accepted This conserves supply current so that the LNR store contents may be retained OFF-HOOK STATE When the HSW input goes high, the MASK output immediately goes to the logic `1' level and remains there until going on-hook or signalling a TBR, (see timing diagram). COLUMN outputs also go high until a key is pressed The oscillator circuit remains inactive until a key is pressed, and is normally off whenever timing functions are not required.

KEYPAD OPERATION A single contact, normally open keypad is required When off-hook the COLUMN outputs are normally held high and the ROW inputs are low. When a key is pressed this connects a COLUMN output to a ROW input and the ROW input is pulled high This action initiates keyboard scanning. During keyboard scanning, the COLUMN outputs are normally low but generate scanning pulses at 7ms intervals on each output in sequence. A key is accepted as valid when, two successive scanning pulses from the same COLUMN are seen on a ROW input. Hence, the minimum bounce-free key closure period which is necessary to guarantee detection is about 14ms (plus the oscillator start-up time if it was not already running).

TONE: Change dialling mode from LD to DTMF * This key is only available as a mask variant. TBR: Timed Break Recall (Flash). LNR: Last Number Redial.


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