Unable to route analogue comparator in PSOC-61xx

[Mrinal]

Hi,

I have placed an ADC with 12 channels and an analog comparator in PSOC-6 design. However the router always fails and is unable to path for routing the analog comparator.

Routing has always been an adventure in all the PSOC devices and we can never tell whether a design will or will not be successfully routed. Or what is the criteria for guaranteed routing success?

I guess the comparator can be routed through analog mux to any desired port. Then why am I getting routing issues? Also, is there a way to manually route the path instead of letting the auto-router decide?

Please help

[Len_CONSULTRON]

Mrinal,

Can you share your project with the forum?

[DennisS_46 · Accepted solution]

Mrinal:
I placed single-ended 12 input SAR and 2 comparators, then let the auto-router work. The analog route view shows:

Pins 1 to 8 use port 10. Pins 13-16 use direct connections to the comparator(opamp) inputs on Port 9. Pins 9 to 12
use Port 9 pins that are not dedicated to opamp inputs. Notice that routing used both analog mux buses. This is
not a requirement, but the routing engine is not quite smart enough to route onto a single analog mux bus.
The comparator outputs route to digital pins, shown on the bottom of the analog routing diagram.
It's also possible to use LPComparators instead of opamp-based comparators if you don't need speed; these have
direct inputs on Ports 5 and 6. The LPComps can also connect to the analog mux buses if you needed to make a
multiplexed comparator. This is not possible with the opamp-based comparators because the SAR MUX already
uses the analog mux buses. The LPComps are separated on the analog mux buss by 'bus breakers' in the route.

If you still don't have success, post the project either on the forum or by private connection. Len is happy to look
at it, so am I.

---- Dennis Seguine
PSoC Applications Engineer

[Mrinal]

Dear Dennis,

Thank you for the detailed reply. My design routed successfully after unlocking all analog nets and rerouting it. The issue was that one of the comparator input was taken from port-10 which is connected to SARBUS. After unlocking, the auto router placed that pin on some other port.

Although it solves the problem, I still have a few doubts.

1. Why did the routing fail when the comparator input or LP_Comparator (I tried both) was connected to port 10.  Port 10 is connected to both SARMUX and AMUX. So the ADC input should use SARMUS and the comparator input should use AMUX. But it doesn't work.

2.  As you mentioned in the reply:

" The LPComps can also connect to the analog mux buses if you needed to make a
multiplexed comparator. This is not possible with the opamp-based comparators because the SAR MUX already
uses the analog mux buses. The LPComps are separated on the analog mux buss by 'bus breakers' in the route."

I absolutely did not understand this. And probably I am missing something big if I wasn't able to understand. Since last few years I have never been able to figure out the analog routing clearly. 

What I am able to understand from PSOC datasheet is that:

- There are two analog MUX that span through multiple ports.

- Any number of analog components can be placed on "any pin" and routed internally to "any other" analog component as long as it is on the analog bus.

But this doesn't happen. AMUX BUS limit? Not even sure what the circuit breaker is used for?

It will be very helpful if you could please explain a bit more on this.

Thank you

[Len_CONSULTRON]

Mrinal,

It appears from your previous post that you are either familiar with the PSoC5 or PSoC3 parts.

These parts have significant flexibility about assigning any digital or analog input to ALMOST any GPIO pins.

Sadly, Cypress decided with the PSoC6 to limit routing GPIO flexibility.  There are good reasons for this limitation.

This means you need to prototype your HW and SW before committing to production PCB.   However, this is not a new concept since for virtually all other MPUs from other vendors you need to do this too.

[DennisS_46]

Mrinal:
I attached the simplest possible project that shows standard routing. You can see in the analog routing diagram that Port10 can connect to the SARMUX bus, that vertical row of switches. In that vertical row are switches that connect to the AMUX buses. The Comparator pins on Port9 connect to P0.9, 9.1, 9.4, and 9.7. That leaves P9.2, 9.3, 9.5, and 9.6 which will be connected to the AMUX bus for SAR inputs. You could put in 16  more SAR inputs on Port11 and Port12 and further around the chip.
LPComps can be placed for direct inputs on Port5 and Port6 without using the AMUX buses. If you wanted to do a multiplexed LPComp that is possible but the bus-breakers must be opened in order to isolate that portion of the AMUX bus from the section used to route Port9 to the SAR. 
Cap sense can be used on Ports 5 and 6 and others on the left side of the schematic . . . but this
requires use of the bus breaker to separate SAR muxed inputs from the CapSense connection.
If you want LPComps AND CapSense, then the LPComp inputs must be direct (i.e., not connected to the AMUX buses) so that they don't interfere with CapSense.

If you want Comparator connection to a signal and the SAR connected to the same signal, they unfortunately can't be connected to the same pin, the routing engine is not that smart. If you want Comparator connection and SAR on same signal, they must be on separate pins. 

If you want to discuss this further, set up a zoom or webex meeting where we can share stuff on screen. Contact me at dennis.seguine@infineon.com. I work US Pacific time zone.

---- Dennis