I've got an ENC28J60 Ethernet Controller in a circuit I'm building. I was testing it out but when I got to the point of talking to it over SPI with my micro-controller I got utter silence back from the device.
I got a 'scope out and sure enough, the the SCK and MOSI pins on the device are wiggling the way I expect them to while the /CS pin is driven low, but the MISO signal is flat-lined at GND (all measured at the pins of the ENC28J60). So I got to looking at the solder joints on the device more closely (using an SMD package). I saw that I had a subtle bridge between two of the pins: VCAP and VSS!
So I went back to the soldering station and remedied the bridge and headed back to the 'scope. Still not working, but doing something different (progress!?). Now when the SCK signal fires away, the MISO signal does "react," just not as I'd expect. The signal has a "wiggling characteristic" that is correlated with SCK, but it's certainly not what a digital output should look like, and voltage levels go negative to about -100mV, and never exceed 0V.
On to the question. What is the impact of having grounded VCAP? Is the chip fried? What is the explanation for the negative quasi-inverted quasi-digital output on the MISO line?
Edit
I measured (with a 'scope) every pin of the ENC28J60. Why would the crystal not be ringing? Anything else look out of the ordinary?
+-------+----------+-------------------------------+
| Pin # | Name |Measurement Result |
+-------+----------+-------------------------------+
| 1 | VCAP | 2.66VDC (760mv P-P @ 4.15MHz) |
| 2 | VSS | GND |
| 3 | CLKOUT | GND |
| 4 | /INT | 3.3V |
| 5 | NC | 3.3V |
| 6 | SO | Noisy/Negative Digital Signal |
| 7 | SI | 0V/3.3V Digital MOSI Signal |
| 8 | SCK | 0V/3.3V Digital SCK Signal |
| 9 | /CS | 0V/3.3V Chip Select Signal |
| 10 | /RESET | 3.3V |
| 11 | VSSRX | GND |
| 12 | TPIN- | 1.08V (floating) |
| 13 | TPIN+ | 1.08V (floating) |
| 14 | RBIAS | 1.28V |
| 15 | VDDTX | 3.3V |
| 16 | TPOUT- | 3.3V |
| 17 | TPOUT+ | 3.3V |
| 18 | VSSTX | GND |
| 19 | VDDRX | 3.3V |
| 20 | VDDPLL | 3.3V |
| 21 | VSSPLL | GND |
| 22 | VSSOSC | GND |
| 23 | OSC1 | GND (hm...) |
| 24 | OSC2 | GND (hm...) |
| 25 | VDDOSC | 3.3v |
| 26 | LEDB | GND |
| 27 | LEDA | GND |
| 28 | VDD | 3.3V |
+-------+----------+-------------------------------+
Best Answer
VCAP is the 2.5V reference of the IC. It's internally generated from the 3.3V supply.
There's a telling footnote under the "Absolute Maximum Ratings" table:
The most important part of that is: "not designed to supply an external load". Your short circuit was a significant external load.
If VCAP hasn't recovered after the external short was removed, replace the IC. Even if VCAP is OK, if you can't get correct behaviour on MISO and you have any doubts, replace the IC.