Monitor MISO without driving CLK

[dietrichwall]

Hi,

i´m using the LPC2132 MCU in combination with TIs ADS1018 ADC.

The ADC will drive the MISO low whenever conversion results are ready and the ADC is selected with CS. The Problem is, that CLK should not been driven in this time, or the ADC will clock out the last buffered result. Is there a way in LPC 2132 to see if the MISO goes low without any SPI Transfers, or do I have to reconfigure the MISO Pin as GPIO to monitor the State of the Pin?

Another question: Chapter 6.3 in User Manual mentions :"Selection of a single function on a port pin completely excludes all other functions otherwise available on the same pin".

Does it mean also the GPIO is deactivated?

Unfortunately I cannot test it the next days, because there are some changes on my PCB

Thanks in advance

[dietrichwall · Accepted solution]

Thank you Carlos for you Suggestions,

Afterwards I found some different solution for this: From the user Manual 8.4.3 IOPIN Register: "The register will give the logic value of the pin regardless of whether the pin is configured for input or output, or as GPIO or an alternate digital function."

With that knowledge, the task was very simple.

It seems that IOPin register doesn´t belong to the GPIO Function, in terms of the Chapter 6.3

[CarlosCasillas]

Hi Dietrich,

If you refer so register descriptions of “Pin Function Select Register n” of the LPC2132 User Manual, you will see that GPIO functionality is also selectable, so, if SPI functionality is selected, GPIO is not available.

Besides, after checking Figure 15 “16-Bit Data Transmission Cycle” of the mentioned ADC’s datasheet, it seems that the required functionality could be implemented by two ways:

• Connecting additional GPIO pin in parallel with MISO, in order to be able to detect the falling edge when the CS pin is high.
• Sending the conversion request, and considering the conversion timing, apply a wait state on SPI communication, in order to ensure the conversion competition and then reading back the conversion value.

Hope this will be useful for you.
Best regards!
/Carlos
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[dietrichwall]

ADC is connected to the SPI0, but maybe its still possible to change it to the SPI1/SSP module