Post by thread:[PIC]: Replacement for CF745

I have a commercially made LED "Light Show" based on a Microchip CF745-04/P. I don't like the display patterns it does (it has about 20 display patterns and does each one for about 20 seconds before moving onto the next -- almost any of the 20 would be good if it stuck with it), so I want to replace the chip with one with my own code. A quick websearch leads me to believe this chip is identical to the 16C54. Is this right and, if so, why have 2 part numbers? What would be the best flash-based pin-compatible replacement for this chip? I was originally going to use a 16F628 but then I realized the 16F628 doesn't have an RC oscillator mode which the original circuit uses. I'm now looking at using the hated 16F84. Is this a good option here? In the RC oscillator section, the datasheets say if you change this device, verify the oscillator characteristics. It also says this information is in the Electrical Characteristic section. I can't find the frequency based on the RC values anywhere in either datasheet. It uses a 5k resistor and 20pF capacitor. Where can I see what frequency the chip will run at, and will the 16F84 have the same speed with this configuration as the CF745? Thanks, Jason

CF745 and some other CF7xx parts are untested 16C5x parts specifically made for mainland Chinese market to combat the Taiwanese clone which is really cheap (US$0.3 to US$1 for clones of PIC16C5x and PIC16C7x). They are supposed to be not available to the general public. 16F54 is of course the replacement of choice. :) Anything is better than 16F84. :) Since it is using RC oscillation, the best option is to check OSC2/ClockOut which has the frequency of Fosc/4. Take note to use a low capacitance probe if directly probing OSC1/ClockIn pin since typical probe capacitance of 10pF will load the circuit. More over if you read the manual, you will know that 20pf and 5k will translate to roughly 3.8Mhz with 5V supply. You do not even need to measure. Regards, Xiaofan {Original Message removed}

> I was originally going to use a 16F628 but > then I realized the 16F628 doesn't have an RC oscillator mode > which the original circuit uses. are you sure is does not? > It uses a 5k resistor and 20pF capacitor. Where can I see > what frequency the chip will run at, and will the 16F84 have > the same speed with this configuration as the CF745? why not change to the internal oscillator, a resonator, or even a crystal? Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu

On Aug 15, 2005, at 1:33 AM, spam_OUTpicTakeThisOuTcanadaspeaks.com wrote: > What would be the best flash-based pin-compatible replacement for > [16C54]? I was originally going to use a 16F628 but then I realized > the 16F628 doesn't have an RC oscillator mode which the original > circuit uses. Huh! While the 628 only has an "external R" oscillator option, the 628A has the typical external RC oscillator... There is also the new-ish 16F54, aimed at direct (flash) replacement of the 16C54 (very cheap.) BillW

From: "Wouter van Ooijen" Sent: Monday, August 15, 2005 2:05 AM > > I was originally going to use a 16F628 but > > then I realized the 16F628 doesn't have an RC oscillator mode > > which the original circuit uses. > > are you sure is does not? I was looking for an RC mode to so the chip would work as a drop-in replacement for the one the original manufacturer used. The 16F628 has an internal RC mode. > why not change to the internal oscillator, a resonator, or even a > crystal? I don't want to use a resonator or crystal because I don't want to have a rat's nest of components stuck to the circuit board. Using the internal oscillator might be a better idea than sticking with the RC mode. Would I just pull the resistor and capacitor from the PCB? I got the item as new surplus very cheaply because the transistors that drive the LEDs are severely underrated. They're TO-92 packages with what I think are house numbers, and they have to drive up to 400mA. They get so hot I think it's a fire hazard. I was going to try using a PCM output to have the LEDs on 70% of the time they're supposed to be and see if it runs much cooler without losing too much brightness. From: "Chen Xiao Fan" <.....xiaofanKILLspam@spam@sg.pepperl-fuchs.com> Sent: Monday, August 15, 2005 1:59 AM > CF745 and some other CF7xx parts are untested 16C5x parts specifically > made for mainland Chinese market to combat the Taiwanese clone which > is really cheap (US$0.3 to US$1 for clones of PIC16C5x and PIC16C7x). > > They are supposed to be not available to the general public. I think I've read about these chips years ago and forgotten. I didn't realize that's what I had. > 16F54 is of course the replacement of choice. :) Anything is better > than 16F84. :) Why would the 16F54 be better than the F84? There seems to be very little difference between these chips. > More over if you read the manual, you will know that 20pf and 5k > will translate to roughly 3.8Mhz with 5V supply. You do not even > need to measure. I was looking in the manuals for the C54 and F84 and couldn't find that information. That is exactly what I needed to know though, so thank you. Jason