Using P31 after initialization

Vega256 · 2012-07-28 12:31

Hi guys,

It turns up that all of my Prop pins are booked...except for the last four pins. I need more pins (at least one), but initialization signals really mess things up when my circuit is powered on. I am trying to use P31, but I don't think it's working the way I had thought it would work.

P31 is an input during initialization; it receives from the PC. The line I want connected to it is an output which is initially LOW.

Wouldn't the Prop take that to mean that there no PC connected, and to just continue loading from EEPROM?

Mike Green · 2012-07-28 13:05

Yes, P31 low means that there's no PC talking to the Propeller since this is a normal serial input which idles at high. There is a timeout involved ... You'd have to look at the published ROM bootloader to see how much time is involved. How are you going to handle debugging your hardware and software? Best thing would be to have a jumper that selects P31 between your sensor and a programming connector. Alternatively, you could use an OR gate, whether an IC or a diode OR with a pulldown.

Vega256 · 2012-07-28 13:15

Mike Green wrote: »

Yes, P31 low means that there's no PC talking to the Propeller since this is a normal serial input which idles at high. There is a timeout involved ... You'd have to look at the published ROM bootloader to see how much time is involved. How are you going to handle debugging your hardware and software? Best thing would be to have a jumper that selects P31 between your sensor and a programming connector. Alternatively, you could use an OR gate, whether an IC or a diode OR with a pulldown.

Ah, thanks, Mike. It could be a problem with my code, too. I'll chime back in later.

Vega256 · 2012-07-28 13:47

              mov       address, ina                      'Obtain the address and data 
              mov       data, ina
              mov       temp, ina

              shr       temp, #17
              and       temp, addressFilter2        
                                    
              shr       address, #8                       'Adjust address to proper position
              and       address, addressFilter            'Filter out unwanted pin states
              or        address, temp
                                
              and       data, dataFilter                  'Filter out unwanted pin states

storeData
              add       baseAddress, address            'Obtain the indexed address
              wrbyte    data, baseAddress                      'Write data to the indexed address
              xor       outa, wait_pin
              waitpeq   cs_pin, cs_pin                      'Wait until chip select signal goes inactive
              jmp       #monitor

This is an excerpt from a program. Connected to the Prop [P8-P21] are address lines [A0-A13]. I need one more line [A14] to get fed to the Prop (hopefully through P31...). Because A14 won't come after A13 on the Prop, I guess I have some bit shifting to do. With A14 connected to P31, this is the code I have. Should 'address' hold the correct address after the shifting and masking?

kuroneko · 2012-07-28 17:25

Vega256 wrote: »

This is an excerpt from a program. Connected to the Prop [P8-P21] are address lines [A0-A13]. I need one more line [A14] to get fed to the Prop (hopefully through P31...). Because A14 won't come after A13 on the Prop, I guess I have some bit shifting to do. With A14 connected to P31, this is the code I have. Should 'address' hold the correct address after the shifting and masking?

Logic looks OK. If you can afford to use flags (carry that is) may I suggest another way?

mov     address, ina                                                   
                mov     data, ina
[COLOR="silver"]'{opt, wrbyte}  and     data, dataFilter                ' Filter out unwanted pin states[/COLOR]

                shl     address, #10 wc                 ' align with MSb, carry := address[31]
                rcr     address, #1                     ' collect A14
                shr     address, #17                    ' Filter out unwanted pin states

This gets rid of all three filter masks (dataFilter is not required due to wrbyte usage) and some code.

Vega256 · 2012-07-28 21:40

kuroneko wrote: »
Logic looks OK. If you can afford to use flags (carry that is) may I suggest another way?
mov     address, ina                                                   
                mov     data, ina
[COLOR=silver]'{opt, wrbyte}  and     data, dataFilter                ' Filter out unwanted pin states[/COLOR]

                shl     address, #10 wc                 ' align with MSb, carry := address[31]
                rcr     address, #1                     ' collect A14
                shr     address, #17                    ' Filter out unwanted pin states
This gets rid of all three filter masks (dataFilter is not required due to wrbyte usage) and some code.

Thanks, kuroneko. That looks to be much better.

Using P31 after initialization

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