13.2. Modular Instruments 725
A.4 SignalTransport
Each NIM module has several signal and data I/O ports available on front and rear
panels. The connection can be made through BNC, LEMO, or SMA connectors. The
choice of cable is highly application dependent but for typical applications coaxial
cables are generally used. For transporting digital signals, sometimes using a flat
ribbon cable is more advantageous and space saving.
13.2.BCAMACStandard
CAMAC is an acronym of Computer Automated Measurement And Control. This
standard was originally defined in 1969 by the ESONE Committee and was later
on jointly standardized by the NIM and ESONE committees. With its built-in
controllers and interface capabilities, CAMAC provides a more versatile architec-
ture than NIM, though at the expense of much more complicated and difficult cus-
tomization. The standard CAMAC backplane is called DATAWAY, which can be
directly interfaced to a computer. This feature of CAMAC system makes it far
more advantageous over its NIM counterpart where backplane does not have this
functionality. In this way one can talk to any module in the crate through simple
CAMAC commands without the need to connect it directly to a computer.
B.1 CAMACLayout
CAMAC modules are housed in a CAMAC crate, which can accommodate up to 24
normal CAMAC modules. Each module slot is called astation. Besides these 24
stations there is another one reserved for the crate controller module. The controller
module is an integral part of the system and can not be replaced by some other
module. Also, some controller modules have double widths and therefore take up two
slot positions. In such a case the crate can accommodate up to 23 normal modules.
The pin allocation of one of these 23 normal stations is shown in Fig.13.2.2.
As mentioned earlier, the backplane of a CAMAC crate is called DATAWAY.
DATAWAY consists of not only control, data, and bus lines but also module power
lines. These lines are connected to the modules through sockets. There are standard
guidelines for the current consumption at these sockets. The current should not
exceed more than 3Aat any of the sockets. Furthermore the power dissipation
per station should not exceed 8W. However this rating can be relaxed in certain
situations up to a maximum of 25W. The power rating for the whole crate is 200
W.
B.2 CAMACControllers
A data acquisition system may consist of more than one CAMAC crate. The modules
in each of these crates are controlled by individual crate controller modules. These
modules are connected to a Branch Driver through a parallel Branch Highway. Each
of the crate controllers can be identified on the Branch Highway through this driver.
The Branch Driver is directly connected to a data acquisition computer, which can
be programmed to issue the control commands.