topic Re: Switch matrix clock cycle count in LPC Microcontrollers

Switch matrix clock cycle count

lpcware — Wed, 15 Jun 2016 17:06:54 GMT

Content originally posted in LPCWare by cosborne2000 on Tue Jun 17 08:44:28 MST 2014
I'm new to the ARM Cortex and writing a driver for FTDI's FT1248 bus.
The potential problem is that the FT1248 bus uses a MIOSIO line so the SPI interface isn't standard. Using the hardware SPI (no bit-banging), I'm hoping to accommodate the direction change by using the switch matrix to move the MOSI line "out of the way" during the master read portion (LPC15 is the master).

My strategy is:
1- switch matrix places MOSI on MIOSIO pin
2- LPC15 writes data to FT1248 bus
3- switch matrix places MISO on MIOSIO pin and moves MOSI to another pin (maybe 255?)
4- LPC15 reads data from FT1248 bus.
note: read only transactions won't need this pin movement.

A few questions I couldn't find in the documentation:
How many clock cycles does the matrix use to complete the pin connection?
Can I move peripheral pins while the peripheral is enabled?
Does moving a function to position 255 (default) basically disconnect the function?

Re: Switch matrix clock cycle count

lpcware — Wed, 15 Jun 2016 17:06:55 GMT

Content originally posted in LPCWare by mc on Tue Jun 17 11:14:00 MST 2014
Hi cosborne2000,
Please see below the answers.

Quote:
How many clock cycles does the matrix use to complete the pin connection?

It will take 3 cycles including PINASSIGN register write.

Quote:
Can I move peripheral pins while the peripheral is enabled?

Yes you can move it.

Quote:
Does moving a function to position 255 (default) basically disconnect the function?

yes writing 255 will make pin as GPIO and disconnect the function

Re: Switch matrix clock cycle count

lpcware — Wed, 15 Jun 2016 17:06:56 GMT

Content originally posted in LPCWare by cosborne2000 on Tue Jun 17 12:15:41 MST 2014
Thank you for the information.
One small clarification: is there any issue with assigning several enabled output functions to position 255?
Is 255 a special case that disconnects the function from everything else?

Re: Switch matrix clock cycle count

lpcware — Wed, 15 Jun 2016 17:06:56 GMT

Content originally posted in LPCWare by mc on Tue Jun 17 14:18:18 MST 2014
Hi cosborne,
No there is no problem. Infact default value of the PINASSIGN registers is also 0xFF.