Hardware Projects » E1/T1 Hardware Interface (including icE1usb)

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h1.  osmo-e1-xcvr

This is a simple hardware project that aims to generate a reusable module for interfacing E1/T1/J1 lines from various custom FPGA/CPLD/microcontroller projects.

The board contains tranformers, the analog circuitry, the LIU (line interface unit), an oscillator as well as an integrated transceiver chip.

It exposes the control interface (SPI) as well as the decoded synchronous Rx/Tx bitstreams each on a 2x5pin header.

Framer, Multiplexer, HDLC decoder or anything like that is out-of-scope for now.  The idea relaly is to provide an interface as low-level as possible.

One of the ideas is to create a "soft E1" interface, where the Rx/Tx bitstreams are interfaced with the SSC of an AT91SAM3S and subsequently passed into a PC via USB.  The 2Mbps signal is very low-bandwidth, so that a pure software implementation should be absolutely no problem for todays computing power.

h2. Status

The project is in design phase.  Initial design has finished, but needs to be reviewed.  First prototype PCBs are evaluated since January 12, 2012

h2. Hardware pictures

h3. Bare PCB

!{width:50%}osmo-e1-xcvr-pcb.jpg!

h3. Populated PCB

!{width:50%}osmo-e1-xcvr.jpg!

h2. Hardware Documentation

h3. JP2: TDM interface

JP2 contains the serial TDM bitstream + clock for Rx and Tx direction.  The signals are

|_.Pin|_.Name|_.Description|

|1|GND|Ground|

|2|nRST|low-active reset line, uC can reset the transceiver by pulling this low|

|3|NC||

|4|LOS|Loss of Signal|

|5|TDN|Transmit Data Negative|

|6|RCLK|Receive Clock|

|7|TD/TDP|Transmit Data / Transmit Data Positive|

|8|RD/RDP|Receive Data / Receive Data Positive|

|9|TCLK|Transmitter Clock.  Depending on JP9, this is an input into the board, or an output|

|10|RDN/CV|Receive Data Negative / Code Violation|

h3. JP1: SPI control

This is how the external microcontroller can control the transceiver chip.

|_.Pin|_.Name|_.Description|

|1|VCC_IN|Vcc input, board can be supplied form here if SJ2 is closed|

|2|GND|Ground|

|3|NC|Not connected|

|4|nINT|low-active interrupt output, when transceiver wants to interrupt uC""|

|5|NC|Not connected|

|6|NC|Not connected|

|7|SDO|Serial Data Out (MISO)|

|8|SDI|Serial Data In (MOSI)|

|9|SCLK|Serial Clock|

|10|nCS|low-active chip-select of the SPI|

h3. JP9

JP10 switches the master clock (MCLK) of the transceiver between two on-board oscillators

of 2.048 MHz and 1.544 MHz.  This is required for selecting between E1 or T1/J1 mode.

|_.Closed|_.Frequency|

|1-2|2.048 MHz (E1) mode|

|2-3|1.544 MHz (T1/J1) mode|

h3. JP10

This jumper decides if the 2.048/1.544 MHz MCLK should also be used as TDM Transmit Clock.

|_.State|._Meaning|

|closed|use MCLK as TCLK source, TCLK pin on JP2 is output|

|open|external circuit provides TCLK on JP2|

h3. JP3 + JP4

JP3can be used to supply power to the board.

h2. show me the code

http://cgit.osmocom.org/osmo-e1-xcvr/

h2. TODO list

* hardware

** make ridiculously large test pads smaller

** move C1 closer to U1 VDDIO pad (19)

** remove $ sign from component names

** define which value C5 should use

** mark pin 1 of J1 / J2 on copper + silk screen

** different footprint for L1 ?  value ?

** JP10 is a big too close to J1

* software

** implement minimal SPI driver to initialize transceiver chip