Product Description

The CAMAC Type A–2 crate controller has 2 functions; it has all the features of the Type A–1 standard parallel Branch Highway Crate Controller, defined in IEEE 569/EUR 4600, and is also an ACB Master as in IEEE 675/EUR 6500.

The method originally defined for interconnecting CAMAC crates, via a 65–pair parallel highway, was based on each crate being controlled by a Type A Crate Controller, later amended to the Type A–1 in 1972. This has the command set given in Table 1, and has two front–panel Hughes 132–way connectors with the pin–out given in Table 2, and a rear panel 52–way double density connector for LAM signals going to and GL (Graded LAM) signals returning from a separate LAM Grader module (or strapped connector) whose pin–out is given in Table 3. The Type A or A–1 is driven from a Branch Driver (or in Hytec System terms a Branch Coupler) using asynchronous 4–pass handshake signals TA and TB (see EUR 4600). The logic OR of the GL signals returning from the LAM grader is the Branch Demand, and uses a dedicated Branch Highway line. The response to this of the processor, via the Branch Driver or Coupler, is normally to send an N(30).F(0)(Grant GL) command – see Table 1 – to all on–line Type A’s on the Branch, which reply by gating their individual GL pattern onto the 24 Read–Write lines of the Branch Highway for analysis elsewhere.

Type A Crate Controller

When CAMAC was first specified, only one crate controller could operate in each crate, and it was left to individual suppliers to devise ways of overcoming this problem: for example, the Hytec System Crate which was devised in 1971.

In response to a requirement for a non–proprietary method EUR 6500 and its equivalent, IEEE 675, were published in 1975, In this scheme an external ACB (Auxiliary Control Bus, see Table 4 joins Auxiliary Controllers occupying the right–most stations of the crate (and thus having access to the N and L lines at the Control Station as well as the R/W lines etc.

The method of arbitration normally used with the ACB is Request–Grant or R/G.

Each device that may require to control the crate (and this includes the crate itself) has a front panel coax LEMO labelled ’Request’ which is commoned with the Request line in the ACB, and a pair of LEMO’s labelled ’Grant In’ and ’Grant Out’.

One of the devices in question, with the highest priority, has its Request socket linked (externally) to its Grant In, and its Grant Out LEMO linked to the Grant In of the next highest unit in priority and so on. When one of these units wants to control the crate it asserts Request (RQ) and eventually receives Grant In, possibly via other controllers’ Grant In – Grant Out (internal) links and the Request line of the ACB. It then ’captures’ the Grant signal (i.e. doesn’t allow it to pass on to the next controller) and asserts ’ Request Inhibit’ (R1) on the ACB, which inhibits other devices from asserting Request. Thus by this means, if several devices produce Request at once, the highest priority one of them along receive Grant In and can do its cycle. When done, it releases R1, allowing access to the others.

As an alternative, one (only) of the devices needing access may assert the ACB signal ’ACL’ or Auxiliary Controller Lock–out. This forces all other devices to refrain from asserting Request, and if one of them is actually mid–cycle it must proceed to completion unless it has not yet set S1, in which case it must abort the cycle, thus ensuring the dataway is free for use by the ACL source.