Author Topic: Minimum 80C517 circuit for some activity?  (Read 5514 times)

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Offline rxraineTopic starter

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Minimum 80C517 circuit for some activity?
« on: March 03, 2024, 11:51:42 am »
Hi,
I've made a breadboard circuit using an 8031, and now I've transferred the design to a PCB using an 80C517 to play with the extra bells and whistles that chip comes with. As it's my first attempt at a PCB this complex, I'm building the circuit one step at a time. So far, I have:
  • 5.2V measured across both pairs of power pins on the MCU.
  • EA# tied to GND to use external memory.
  • 20pF capacitors between the XTAL pins and GND, and an 11.0592MHz crystal across them. I have clean sine waves on both XTAL pins: XTAL1 between 0 and 5V, XTAL2 between 1V and 4V. I think this suggests the chip's oscillator circuit is working?
  • 10µF between 5V and reset, and 8K2 between reset and GND. ~0.2V on reset when steady.
I expected to get some activity at this point: at least ALE and PSEN# at ~2Mhz, but they're both steady at Vcc. So far I've tried the following:
  • Tied HWPD# (hardware power down) and OWE (oscillator wtachdog enable) to Vcc, as the datasheet doesn't explicitly state what happens if they float. PE#/SWD is unconnected as the datasheet states this is pulled high and so disables the power savings modes - it measures ~Vcc so I think it's overriding HWPD# and OWE anyway.
  • Tied P0 to GND through 1k resistors, thinking this would feed endless NOPs into any databus read.
Now I've run out of ideas and I'm hoping some kind soul with more experience than I can offer some advice.  :) Is there something I've not done, or an answer in what I've explained that I've missed?
 

Online retiredfeline

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Re: Minimum 80C517 circuit for some activity?
« Reply #1 on: March 03, 2024, 12:41:10 pm »
Why not add the 373 address latch and an EPROM with a short program and see if they get used? Only a couple more parts.
 

Online pcprogrammer

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Re: Minimum 80C517 circuit for some activity?
« Reply #2 on: March 03, 2024, 01:04:11 pm »
Hi,
I've made a breadboard circuit using an 8031, and now I've transferred the design to a PCB using an 80C517 to play with the extra bells and whistles that chip comes with. As it's my first attempt at a PCB this complex, I'm building the circuit one step at a time. So far, I have:
  • 5.2V measured across both pairs of power pins on the MCU.
  • EA# tied to GND to use external memory.
  • 20pF capacitors between the XTAL pins and GND, and an 11.0592MHz crystal across them. I have clean sine waves on both XTAL pins: XTAL1 between 0 and 5V, XTAL2 between 1V and 4V. I think this suggests the chip's oscillator circuit is working?
  • 10µF between 5V and reset, and 8K2 between reset and GND. ~0.2V on reset when steady.
I expected to get some activity at this point: at least ALE and PSEN# at ~2Mhz, but they're both steady at Vcc. So far I've tried the following:
  • Tied HWPD# (hardware power down) and OWE (oscillator wtachdog enable) to Vcc, as the datasheet doesn't explicitly state what happens if they float. PE#/SWD is unconnected as the datasheet states this is pulled high and so disables the power savings modes - it measures ~Vcc so I think it's overriding HWPD# and OWE anyway.
  • Tied P0 to GND through 1k resistors, thinking this would feed endless NOPs into any databus read.
Now I've run out of ideas and I'm hoping some kind soul with more experience than I can offer some advice.  :) Is there something I've not done, or an answer in what I've explained that I've missed?

This will keep the MCU in reset state. Nothing will happen as long as reset is low. The capacitor needs to be between ground and reset and the resistor needs to be between +5V and reset for it to work.

Edit: Added the manual. See page 36 for more info.
« Last Edit: March 03, 2024, 01:07:34 pm by pcprogrammer »
 
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Offline rxraineTopic starter

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Re: Minimum 80C517 circuit for some activity?
« Reply #3 on: March 03, 2024, 01:22:16 pm »
Thank you! I realise now that I copied the reset circuit from the 8031 without noticing the change in sense. When I hold down my "reset" button it pulls high and there's a signal on ALE. Time for some more dirty hacks with the soldering iron...
 


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