Post by thread:CMOS to TTL conversion device

Hi All, I'm working on a project that involves a CMOS camera chip which basically is a CMOS LSI device programmable by a MCU. I plan to interfacing it to a PIC MCU, but before doing that, for testing purpose, I used instead a PC with a general purpose i/o board to provide it with all the necessary address and data signals. However, when I tried to read data from the CMOS chip, the signal originally present on the data line would drop nearly to 0 Volt when the input line from the i/o board touched the output data line of the CMOS chip. My explaination is that the i/o line is a TTL device to which the CMOS chip couldn't provide enough current for normal operation. Hence, if I'm correct, I'll need a CMOS to TTL conversion chip to sit between the i/o line and CMOS chip. Does anyone know if such a device exists? Thanks in advance! John ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com

Hi! Just a thought, but as far as I know... most CMOS outputs are able to drive at least one TTL input. So, check to make sure that your general purpose I/O board is configured for input... ie. not output driving output. Cheers, Don At 02:20 PM 2/18/99 PST, you wrote: {Quote hidden}>Hi All, > >I'm working on a project that involves a CMOS camera chip which >basically is a CMOS LSI device programmable by a MCU. I plan to >interfacing it to a PIC MCU, but before doing that, for testing purpose, >I used instead a PC with a general purpose i/o board to provide it with >all the necessary address and data signals. However, when I tried to >read data from the CMOS chip, the signal originally present on the data >line would drop nearly to 0 Volt when the input line from the i/o board >touched the output data line of the CMOS chip. My explaination is that >the i/o line is a TTL device to which the CMOS chip couldn't provide >enough current for normal operation. Hence, if I'm correct, I'll need a >CMOS to TTL conversion chip to sit between the i/o line and CMOS chip. >Does anyone know if such a device exists? >Thanks in advance! > >John > > >______________________________________________________ >Get Your Private, Free Email at http://www.hotmail.com > >

At 2:20 PM 2/18/99, John Waters wrote: >Hi All, > >I'm working on a project that involves a CMOS camera chip which >basically is a CMOS LSI device programmable by a MCU. I plan to >interfacing it to a PIC MCU, but before doing that, for testing purpose, >I used instead a PC with a general purpose i/o board to provide it with >all the necessary address and data signals. However, when I tried to >read data from the CMOS chip, the signal originally present on the data >line would drop nearly to 0 Volt when the input line from the i/o board >touched the output data line of the CMOS chip. My explaination is that >the i/o line is a TTL device to which the CMOS chip couldn't provide >enough current for normal operation. I'm not sure what the problem is but if the interface is TTL, then I think there must be something else wrong. A TTL input is actually a transistor emitter, so it's difficult for CMOS to pull it low, not high. To make it go high the input just needs to see a high resistance, it will drive itself high. As the dataline is going low the CMOS to TTL conversion is not the problem. There may be something else on the data line that's pulling it low. Perhaps a power or ground problem ? Hence, if I'm correct, I'll need a >CMOS to TTL conversion chip to sit between the i/o line and CMOS chip. >Does anyone know if such a device exists? >Thanks in advance! > >John > > >______________________________________________________ >Get Your Private, Free Email at http://www.hotmail.com

He could use the standard CMOS-to-TTL buffer, a 4950 if I recall correctly. BS At 03:25 AM 2/19/99 -0500, you wrote: {Quote hidden}>At 2:20 PM 2/18/99, John Waters wrote: >>Hi All, >> >>I'm working on a project that involves a CMOS camera chip which >>basically is a CMOS LSI device programmable by a MCU. I plan to >>interfacing it to a PIC MCU, but before doing that, for testing purpose, >>I used instead a PC with a general purpose i/o board to provide it with >>all the necessary address and data signals. However, when I tried to >>read data from the CMOS chip, the signal originally present on the data >>line would drop nearly to 0 Volt when the input line from the i/o board >>touched the output data line of the CMOS chip. My explaination is that >>the i/o line is a TTL device to which the CMOS chip couldn't provide >>enough current for normal operation. > >I'm not sure what the problem is but if the interface is TTL, then I think >there must be something else wrong. > >A TTL input is actually a transistor emitter, so it's difficult for CMOS to >pull it low, not high. To make it go high the input just needs to see a >high resistance, it will drive itself high. As the dataline is going low >the CMOS to TTL conversion is not the problem. There may be something else >on the data line that's pulling it low. Perhaps a power or ground problem ? > > Hence, if I'm correct, I'll need a >>CMOS to TTL conversion chip to sit between the i/o line and CMOS chip. >>Does anyone know if such a device exists? >>Thanks in advance! >> >>John >> >> >>______________________________________________________ >>Get Your Private, Free Email at http://www.hotmail.com > >

Heinz Czychun wrote, quoting John Waters: >> I'm working on a project that involves a CMOS camera chip which >> basically is a CMOS LSI device >> I used instead a PC with a general purpose i/o board ... However, >> when I tried to read data from the CMOS chip, the signal ... would >> drop nearly to 0 Volt > I'm not sure what the problem is but if the interface is TTL, then I > think there must be something else wrong. > There may be something else on the data line that's pulling it low. > Perhaps a power or ground problem ? I'd agree with that. It might take 1.4mA to pull a TTL input low (but good quality I/O cards contain 82C55 which are CMOS and don't load the inputs anyway), but it should be pulled up easily by *any* CMOS device. Do some tracing, use a *multimeter*. Either pins are wrong, cable is wrong ... -- Cheers, Paul B.