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More information on the PIC Testbed I have some questions on the PIC Testbed pub­lished in the January 2001 issue. I know that I have successfully downloaded the program (.asm file) to the testbed (16F84). I assume that I need to set the jumper on the testbed for the clock when programming and I know that the pro­gram was down­loading to the chip (by connecting the LEDs when programming. By the way, if the LEDs are left connected when programming, the chip will not program successfully). But I am unsure as to how to set the program in motion when it is downloaded. Also, I have questions on the COM port on the board. I tried to use the COM port (built onto the board) before realising that it was nearly pointless doing so as it is not supported by any of the software I have tried so far and also because of the differences in support protocol. at pins 11 & 12 of IC1. A larger value will slow down the rate. A smaller value will speed it up. Deep cycle vs auto batteries I’m under the impression that cartype 4WD starter batter­ ies do not like being drained of more than 20% of their capacity. I think that they where intended for starting only and not stor­age. As I have a 4WD and no extra battery, I thought a deep-cycle battery might be better. That way, more Notes & Errata 12/24 Hour Giant Clock, March 2001: as published, in the 24-hour mode the clock changes from 23.59.59 to 24.00.00. This is now changed to the correct 24-hour transition from 23.59.59 to 00.00.00. The upgraded software is called clock1.asm and clock1.hex and is available on the SILICON CHIP website. DI Box, August 2001: the tip contact and integral switch contact in the DC jack socket on the circuit on page 14 are shown reversed; ie, the tip contact www.siliconchip.com.au (M. C., via email). • The program should run (meaning the LEDs should chase) as soon as you disconnect the programming adapter cable and press the reset button. From your description, we assume you have selected the 4MHz crystal as the clock source, which is the correct option for the DEMO & TESTBED programs. We have recently updated the little DEMO & TESTBED pro­grams, as well as created a slightly modified version that will work with the RC oscillator. Regarding the serial port, you’re quite correct in your assumption that you need to download a program to drive the port. A good starting point might be a little terminal program that receives characters from the serial input line and displays them on the LCD. You will find numerous examples to get you started on the ‘net. Check out Microchip’s application notes first at www.microchip.com capacity can be used without damage to the battery. I know that a deep cycle battery would be more expensive. (G. M., via email). • As a general rule, all car and truck batteries have a very poor life expectancy if they are frequently subject to heavy discharge. In normal conditions, the vehicle alternator takes all the electrical load and so the battery does little except for its starting role which normally only causes a brief and very shallow discharge. If you are having electrical problems, the solution may be to install a bigger alternator. should go to switch S1 while the integral switch contact should go to the battery negative. The wiring diagram on page 16 is correct. The parts list on page 19 does not include VR5 which should be a 16mm 10kΩ linear potentiometer. Also the testing instructions on page 19 do not tell how to adjust VR5. To do so, connect a DMM across the bass pot VR2 and adjust VR5 for zero DC voltage. This eliminates any DC current through the bass control and stops it from becoming noisy. 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