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DELETED (Inactive)
6 Posts |
 Posted - Jan 24 2004 : 04:15:48 AM
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Hi,
I have a couple of modems that have chipsets and drivers that support callerid, but the manufacturer left out the CID circuit to cut down on cost so there is no data path between the modem and phone line when it is on hook and ringing. The modem currently uses a wave rectifier circuit to detect rings, but this circuit must filter out the CID info.
I read somewhere that you can add a tiny capacitor in parallel with the ring detection circuit which would allow a data path but not take the phone off hook.
My question is what is the best circuit to enable this data path for callerid. If it is just adding a capacitor. What value and type should I uses for US standard callerid.
Cheers,
hmpho
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 25 2004 : 11:29:49 AM
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CID may be made in several ways, and may require even extra IC. So it is hard to tell how to add it to your modem. Also, it must be supported in the modem firmware. So you may end up with necessity to change datapump chip. The simplest way is just to buy a new modem, they are very cheap now. Down to 0 with rebate.
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DELETED (Inactive)
6 Posts |
Posted - Jan 25 2004 : 11:20:51 PM
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Hi YS,
Thanks for responding. I know I can buy a modem that supports this, but I just wanted to do this for fun and experience rather than just functional reasons.
1) I know the driver supports CID (most of these are HSP modems so the datapump and
Controller are software based anyway).
2) I know the chipset supports CID. The modem is capable of Callwaiting CID just not regular CID because it is missing the required circuit which monitors the line while on hook.
If you have any info on this I would very much appreciate it. FYI most of the cheapo $0-$10 modems that I've seen usually either lack Callwaiting or Distinctive ring. I guest by leaving out one of them they are able to keep cost low. I essentially need a circuit that will allow data to come into the modem without taking it of hook. I've checked the chipset manufacturer website and the chipset and drivers usually supports both.
Cheers,
mpho01
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 26 2004 : 02:07:54 AM
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well, what are markings on the chipset? what is the modem name/manufacturer? There are few odds I may have such an info, but I need to know at least that. You may search for datasheets on the chipset yourself, too.
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DELETED (Inactive)
6 Posts |
Posted - Jan 26 2004 : 6:35:07 PM
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Hi YS,
The chipset is an st7554. The datasheet is at http://home.comcast.net/~hmpho/st7554.pdf. The modem also uses a st7550 and st924. If you look at the second reference circuit design. That is the design that my modem has. Notice, unlike the first reference design the CLID pin (43) is not used. I'm hoping that If I can make a circuit that properly feeds into pin 43 then CID should work.
Let me know what you think.
Cheers,
mpho01
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 26 2004 : 9:43:17 PM
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These two ref.designs are quite different.
In first ref. design, they use silicon DAA (two other chips), which has built-in circuitry for CID. I would check ST75951 datasheet to see what kind of signal they use for CID.
Second design, more traditional, has just a codec and op-amp-based DAA. In this case, you need to provide CID circuitry yourself. There was special chip, made few years ago by Motorola, which provided CID function. It can be On Semiconductor now, if they still make it. I do not remember part number. This chip with some additional elements could probably be what you want.
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DELETED (Inactive)
6 Posts |
Posted - Jan 27 2004 : 01:41:31 AM
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Hi YS,
Am I wrong in assuming that the ST7554 Chip will do the CID decoding for me and that all I need to do is provide the correct data path with the correct signal type?
Cheers,
mpho01 |
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 28 2004 : 07:43:37 AM
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Yes, that's what I mean.
On three-chip design, CID signal comes from GPIO pin of the codec, which shows that it has been processed already. You do not have this capability in two-chip design. CID information is sent between rings, and a special (separate) receiver must be conected to the line all the time (usually through small capacitors) and must be protected from 100VAC ring signal. BTW, rings are not detected by "wave rectifier", but by optoisolator and surrounding elements.
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DELETED (Inactive)
6 Posts |
Posted - Jan 31 2004 : 04:35:14 AM
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Hi YS,
So what circuit is require to connect to the CLID pin. Doesn't the modem already have a circuit in place to protect against the ring current? I know the CID info is transmitted at 1200 baud. I'm still unsure from your answer does the CLID pin receive the CID info from the phone line and decode it or not? Thanks for your time.
Cheers,
mpho01
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 31 2004 : 07:14:18 AM
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Again:
I think you need a separate receiver/decoder to be connected to CID pin. I may be wrong though. But anyway it needs separate protection circuit, aside from ring detector.
From my experience, it is not easy to add something to highly integrated modem. You have to be able to change datapump firmware as well.
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DELETED (Inactive)
6 Posts |
Posted - Jan 31 2004 : 2:37:05 PM
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Thanks,
Would you know of a good simple circuit to perform the ring/voltage protection, but still let the raw CID info through (.ie capacitior/ resistor values).
Cheers,
mpho01
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YS
Nobel Prize Winner
USA
1132 Posts |
Posted - Jan 31 2004 : 10:34:46 PM
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Through.. where?
You need a CID IC. Find one, get datasheet, and use reference schematics.
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Q:Adding CID circuit to modem?
