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D19m Technical Description
Date printed:
30.06.20
D19m E3
1 D19m SYSTEM BASICS
1.1 Introduction
The D19m series consists of single cards with a width of 100 mm (Eurocard
width) that can be plugged into a 19” frame (3 or 1 height units). The out-
put of the input cards feeds a time-division multiplex (TDM) bus. The pur-
pose of this bus is to multiplex all the input signals, so that they can directly
feed a MADI connection (multiplexer unit/MUX) via a MADI interface.
Just the other way round, the signal coming from a MADI connection can be
fed into the TDM bus, too, from where again all output cards can derive
their information (demultiplexer unit/DEMUX). Beyond that, most card
types can be used in standalone applications, too.
TDM Bus The TDM bus is a 16-bit wide bus with 128 time slots. The format is simi-
lar to the AES/EBU format, however distributed in parallel on two words.
This means that 64 audio channels with 24 bits plus additional information
(U-bits, C-bits etc..) can be transferred. The time slot allocation is given by
the card addresses hardwired on the backplane. Thus an A/D converter card
plugged into the first slot automatically gets the address 0 and writes to the
bus only during its own, assigned time slots. Since ADAT and TDIF input
cards occupy multiple channels on the bus, their address must be set with
on-card DIP switches. All remaining cards are 4-channel and can be easily
exchanged, e.g. an analog card may be replaced by a digital card. The clock
signals (CK128, frame and sync) are sent by the MADI card (unless it is
switched to
client
mode) or the MADO card and are distributed on the back-
plane.
The AES/TDM signal selects between standalone and TDM bus operation
for the individual cards. This signal is controlled by the MADI or MADO
card, too. It decides e.g. whether the D/A converter card takes its input sig-
nal from the TDM bus or from the AES/EBU input, or whether the A/D
converter card may write to the TDM bus or not. If individual cards in the
rack should operate in standalone mode, an additional jumper is available on
the backplane in order to interrupt this select signal for every card individu-
ally.
Synchronization Except for the AESI and AESO cards, all cards have a separate sync input.
Depending on the jumper setting, this input receives the sync signal from the
bus (AES/EBU signal with TTL level) or from a separate input (standard
balanced AES/EBU signal according to AES11). Thanks to the AES/EBU
inputs and outputs, the converter cards also can operate in standalone mode.
It is possible to extract a sync signal from the MADI (when using MADI
optical). However, this feature should be used only for large distances and
stagebox systems. Otherwise it is recommended to use the AES/EBU sync
line. This results in a smaller error probability (having two PLLs less in the
path), reduced jitter, and allows the use of variable speed.
Split Rack Configuration A MADI and a MADO card can share the TDM bus in a common "split
rack". The available channels have to be split for MUX and DEMUX chan-
nels. In such a system, using the MADI card’s sync out should be avoided
whenever possible. Since the MADO card is always considered as a master
by the software, a hardware modification is necessary in such a case. There-
fore, it is recommended to use separate racks for MUX and DEMUX (refer
to example in chapter 2.3.1).