Retronetworking » Retro-GSM

h1. TCSM2 ET1TC chassis

This chassis holds up to 8 [[TCSM2_ET_modules|Exchange Terminal modules]], in two banks of 4 modules each. Each half of this chassis (each bank of 4 ET module slots) is completely independent from the other, to the extent that *no* electrical connections are shared between the two halves. Each half of V00 connector (described below) is wired to one bank of 4 slots, and each of these banks has its own power input connector for -48 VDC.

Connector V00 on the external back face of ET1TC backplane is the [[TCSM2_interchassis_cable|interchassis interface]]; if both halves of ET1TC are populated with ET modules, then V00 needs to connect to two different TC1C units (each with its own TRCO card, forming its own TCSM2 logical unit) in order to produce a useful result. Alternatively, if only one half of V00 is wired to a single TC1C backplane in a homebrew setup, then only the corresponding bank of 4 ET module slots can be used.

Whichever half of ET1TC is chosen on the basis of interchassis wiring, if only one ET module is used, it needs to be in slot 0 of that bank, i.e., absolute slot number 00 or 04 as marked in ink on the metal.

Unlike the situation with TC1C chassis, there is no chassis-wide power supply or controller module in ET1TC. Instead each ET module in the chassis is its own rugged entity:

* For power distribution, the backplane implements a power bus on the raw -48 VDC input; each ET module takes in this power and carries its own switching converter(s) to whatever operational voltages it needs.

* For most of the signal interface, each ET module gets its own set of signals on the interchassis interface on V00; for the few signals that are shared by all ET modules in one TC1C-connected bank (but not across banks!), these signals are wired in parallel. These shared signals are unidirectional timing control from TRCO to ET modules and an alarm bus.

h2. Pictures

I (@falconia) snapped some pictures of ET1TC backplane when I had that backplane temporarily unscrewed from the chassis:

https://www.freecalypso.org/members/falcon/pictures/Nokia_TCSM2/ET1TC_backplane/

These pictures were taken right after connector V00 was modded (inside plastic tabs removed) in order to allow the interchassis connection to be made in a homebrew manner. All other connectors (other than V00) still have their plastic tabs intact - the difference should be visible in the photos.