[[hardware]]
== e1-tracer Hardware

The e1-tracer Hardware consists of a single circuit board, mechanically
either assembled into a desktop enclosure (KOH variant) or into a 3U component
carrier module (BGT variant).

image::images/e1_tracer-bgt-front.jpg[width=400,title="e1-tracer BGT variant"]
image::images/e1_tracer-koh1.jpg[width=400,title="e1-tracer KOH variant"]


It's main building blocks are:

* an iCE40 FPGA
* two E1 Line Interface Unit ICs
* two E1 line interface analog (transformers, biasing networks and ESD protection)

=== Schematics / Board Layout

As e1-tracer is an OSHW (Open Source Hardware) project, the full schematics
and design files are publicly available.

The design files in EAGLE format are available at https://git.osmocom.org/osmo-e1-hardware/tree/hardware/e1-tracer

PDF rendered schematics are available at https://gitea.osmocom.org/retronetworking/osmo-e1-hardware/raw/branch/master/hardware/e1-tracer/e1-tracer_sch.pdf

=== Connectors / LEDs

image::images/e1-tracer-plate.png[width=400,title="front side of e1-tracer"]

From left to right, there are the following LED indcators, connectors and buttons:

* LED block with 4 LED's
* Primary E1 Port (E1 A)
* Secondary E1 Port (E1 B)
* Serial Console Connector
* USB Connector
* Bootloader Button

==== LEDs

The left-most column of LEDs consists of two red *LOS LEDs*.
They indicate a LOS (Loss Of Signal) condition for the respective E1 direction.  It is normal for the LEDs to be illuminated even in presence of a valid E1 signal until the host software has fully initialized the firmware for the first time after power-up.

The right column of LEDs consists of two further LEDs:

* a multi-color *STATUS LED* on the top
* a green *POWER LED* on the bottom

The *STATUS LED* is used by the firmware to indicate a variety of status
information.  Pleas see the firmware documentation in <<firmware>>.

The green *POWER LED* is illuminated as soon as the device has DC power.

==== J1A and J1B: E1 Interface Connectors

There are two RJ45 connectors next to each other.

Those are the connections for your symmetric 120 Ohms E1 interface
circuit.  You insert the e1-tracer into your E1 link.  The two ports are
internally wired straight-through, so you can insert the e1-tracer into
your E1 link.

The actual tracing functionality is implemented via a high-impedance
tap, which will not disturb the normal E1 communications link. The link
remains unaffected even if the e1-tracer is unpowered.

.Pin-out of RJ45 E1 connectors
[options="header"]
|===
| Pin | Function (TE) | Function (NT Mode)
| 1   | Pair A        | Pair A
| 2   | Pair A        | Pair A
| 3   | not used      | not used
| 4   | Pair B        | Pair B
| 5   | Pair B        | Pair B
| 7   | not used      | not used
| 8   | not used      | not used
|===

NOTE: E1 cables use RJ45 like Ethernet, but Ethernet cables have a
different pin-out.  Particularly, you cannot use an Ethernet cross-over
cable as an E1 cross-over!

==== X1: USB Connector

The USB connector is a USB Mini B connector.   The e1-tracer uses
USB 1.1 full-speed signals.  As the e1-tracer is a bus-powered device,
5V DC power is also sourced from this connector.

==== X2: Serial Console Connector

The serial console is used for development and debugging.  It uses an
Osmocom-style 2.5mm stereo TRS jack.

The serial console uses 3.3V CMOS logic levels

The serial console uses a rate of 1000000 bps.

The pin-out is as follows:

* Tip: Tx output from PC (Rx input of e1-tracer)
* Ring: Rx input of PC (Tx output of e1-tracer)
* Shield: GND

A compatible cable can be sourced from the sysmocom web-shop at
http://shop.sysmocom.de/.

Note that CP2102 based cables require special programming to support
the baud rate of 1000000 (as opposed to the more standard 921600).

[[hw-pushbutton]]
=== Bootloader Button

There is a push-button next to the _USB B connector_.   It is recessed
to protect against accidental use.   You will need to use a paper clip,
pen tip or other similar object to push it.

The button, when pressed while power-up, can be used to force booting
into the DFU loader in order to recover from a broken firmware
installation.