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Forum Index : Microcontroller and PC projects : PULSE output suitable for clock?
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| alligator Newbie  Joined: 18/10/2014 Location: AustraliaPosts: 3 |
So first of all, I'm new, Hi. I bought the Colour Maximite kit recently, after trying 200 PRINT "HELLO WORLD", I wanted to get it to control a 65C22 I had. That's the updated version of the I/O chip designed for the MOS 6502, a wildly popular 8-bit microprocessor i'm sure most of you have heard of. Anyway, so it needs a clock pulse to run. This one supports up to 14MHz. In its original design, that would be plugged straight to the CPU's clock. I suppose in theory the same could be done here, but I don't have the tools with me to modify the PCB like that. So is it possible to get one of the I/O pins to do this? The manual says PULSE will only run in the background for a pulse of 3mS or more and i'd need it to get as low as 0.00025 for at least 4MHz, which i'm not even sure the program would allow. Am I even going about this the right way? Is PULSE the command I want? Is there some trick to send the micro's clock pin straight to one of the outputs? |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9063 |
6502 - the CPU the Atari 8-bit was built around. The computer I grew up on. 
The clock for the PIC32 on the MaxiMite is derived from the 80MHz crystal, but me thinks that is too fast for your purposes. I would be inclined to simply build a suitable oscillator circuit out of a couple of ceramic caps in the area of 27pF or so, and the wanted crystal, or you could just use one of those three-pin ceramic resonators at 4MHz - that should suffice for the chip, depending on just how critical it is that the reference clock frequency stays exactly where it needs to be - sounds like this chip does not care much, so long as the clock is not faster then 14MHz. Oh, and welcome to the forums.  Smoke makes things work. When the smoke gets out, it stops! |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 5905 |
The best command to use for a background output is PWM but on the Maximite the maximum frequency is 1MHz (550kHz on the Micromite). The simplest and probably the cheapest way is to buy a separate crystal. Jim @Groggy, the Maximite has a 8MHz Xal, not 80! VK7JH MMedit MMBasic Help |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Most if not all of the 65c22 functionality is built right into the Color MaxiMite (CMM) itself. Connecting a 65c22 to the CMM is very inefficient as you need to connect a lot of pins. At least the complete databus (8 bits) and then the addressing bits, r/w signal etc. All those pins needed to connect to the 65c22 could be used directly performing the same functionalities directly from MMBasic. These chips are ideal for microprocessors which have an external address and databus. Microcontrollers like the PIC32 that is used in the CMM has internally a microprocessor core and lots of peripherals already internally connected. The address and databus is completely internal. For connecting a chip like the 65c22 you would need to simulate an address and databus on its output pins, making sure that all signal levels and timings are within specifications. A lot of programming effort for no net gain. When a 65c22 is connected to a 6502 you don't have to worry about that at all as they are matched with each other (bus compatible). I would leave that 65c22 in the obsolete (for use with microcontrollers) parts bin. :) Microblocks. Build with logic. |
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