CMX867A View Datasheet(PDF) - CML Microsystems Plc
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CMX867A Datasheet PDF : 8 Pages
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Calling modem
Detect Unscrambled
ONES in 155±10ms Wait 456±10ms
Scrambled ONES in low band
Data
Connect to
line & dial
Answering modem
Silence
Answertone
2100Hz
Detect
scrambled
ONES in high
band for
270±40ms
Wait 765±10ms
1800Hz Guard Tone*
Unscrambled ONES in high band
Scrambled ONES in high band
Data
2150
±350ms
Connect to
line after ring
validation
3300ms
±700ms 75±20ms
Detect
scrambled
ONES in low
band for
270±40ms
Wait 765±10ms
Fig. 1. V.22 Connect Handshake.
* Guard tones are country dependent
1. V.22 Handshake
Figure 1 above is an adaptation of the V.22 Connect Handshake from Volume
VIII - Fascicle VIII.1 of the Blue Book series published by the ITU (formerly
CCITT) November 1988. The actions taken by the calling and answering
modems are illustrated with flow charts and ‘C-Bus’ command strings for
implementation on the CMX867 – see Figures 2 and 3.
1.1 Points to note
(a) The modem can connect to line by setting the RDRVN output (CMX867 pin
3) to Vss in order to drive a relay or semiconductor switch. The On-Hook
level of RDRVN must be Vdd otherwise spurious line seizures could occur on
initial power up or reset.
(b) Dial tone will be present typically 300ms after going Off-Hook. If dialling
without dial tone detection then a pause of at least 2.7s (max. 8s) should be
introduced before dialling commences. If no dial tone is detected within 5
seconds of going Off-Hook then the modem should return On-Hook.
(c) DTMF digits should be typically 100ms long with 100ms silence gaps in
between.
(d) Figures 2 and 3 are intended to give general guidance on the use of registers.
They do not show software timeout features which avoid lockup on certain
loops. The treatment of interrupts (enabling, servicing & disabling) is not fully
shown since these are options which may be implemented for a particular
design. Guard tones are also not included.
(e) On the General Switched Telephone Network (GSTN), the calling modem
should transmit on the low band and receive in the high band.
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