Microchip Developer Explorer 16/32 User Manual page 9

Explorer 16/32 Development Board User's Guide - Developer Help
it will not be USB compliant. This jumper should be left fully open in USB device
only, USB Type-A embedded host, or non-USB applications, so as to disable VBUS
output sourcing in these types of applications.
J23 – This can be used to disconnect the potentiometer R6 output from the PIM
microcontroller. By default, a trace (on the bottom of the PCB) shorts the two pins of
J23, and the POT will always be connected to the microcontroller. If desired, the
trace can be cut to disconnect the POT, and a 2-pin jumper may optionally be
installed to allow user re-connection/disconnection of the POT.
J25 and J26 – These jumpers are present for USB signal quality reasons. In USB
High Speed (480Mbps) applications, jumpers J25 and J26 should both be left in the
open/uncapped state, in order to avoid degrading the USB signal quality. In
non-USB applications, both jumpers should generally be capped.
In USB High Speed applications, the P89_USBDN and P90_USBDP nets are
implemented as a dedicated transmission line (~90 ohm differential and ~30 ohm
common mode impedance), between the PIM pins 89/90 and the USB connector.
Capping J25 and J26 has the effect of shorting the P89_USBDN/P90_USBDP nets
to the P89_USBDN_E/P90_USBDP_E nets respectively. This allows access to PIM
pins 89/90 on the I/O access headers J46/J47 and the PICtail Plus interface,
enabling them to be used as general purpose I/O pins. However, capping J25 and
J26 creates "T" junctions in the signal traces (trace splitting), which will disrupt the
transmission
communication. At USB Low (1.5 Mbps) and Full (12 Mbps) speeds, the relatively
slow signaling rates (and edge slew rates of the signals) are much more forgiving of
non-ideal trace layout and short (< 19 cm) "T" junctions/signal branches. Therefore,
in Low and Full speed USB applications, J25 and J26 may be left either capped or
uncapped, although for best signal quality it is still preferable, but not strictly
required, to keep both jumpers open.
J27 – Connects the 25LC256 EEPROM (U5) chip select to the PIM P79_EECS net,
when capped. When left open, the resistor R2 de-selects the EEPROM, ensuring
that no I/O contention will occur on the P11_MISOA net, even if the PIM
microcontroller firmware uses this net as a digital output.
J28 and J29 – These three pin jumpers connect to the CC1 and CC2 nets on the
USB Type-C connector. In USB embedded host applications using the Type-C
connector, both jumpers should be capped in the 1-2 position, so that the CC1/CC2
pins of the USB connector are pulled high by R105 and R106. When pulled high,
this advertises to the other USB product at the other end of the USB cable, that a
host is attached/present. When implementing a USB Type-C device
application, the J28 and J29 jumpers should instead by capped in the 2-3 position,
pulling CC1/CC2 low (via R107 and R10). This signals to the host (or hub) at the
other end of the USB cable that a device has been attached (as opposed to another
9 z 18
line characteristics,
http://microchipdeveloper.com/boards:explorer1632
required for reliable USB High Speed
mode
7.6.2017 8:59