Hardware Projects » E1/T1 Hardware Interface

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=  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, Multiplexe,r 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.

== 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

== Hardware pictures ==

=== Bare PCB ===

=== Populated PCB ===

[[Image(osmo-e1-xcvr-pcb.jpg, 50%)]]

== Hardware Documentation ==

=== 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||

=== 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||

=== 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.

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

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

=== JP10 ===

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

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

||open||external circuit provides TCLK on JP2||

=== JP3 + JP4 ===

JP3can be used to supply power to the board.

== show me the code ==

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

== 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