Product Description

The Branch Coupler type BR–CPR–4–1 is a two width Hytec System Crate module which drives a (parallel) Branch Highway in accordance with EUR 4600 (IEEE 596, IEC 552): it must be used in conjunction with an Executive Controller in the right–hand two crate stations plus a suitable Program Source (such as manual controller SC–TST–1 or a computer interface). Thus it forms a link between the System Crate and a Branch Highway (which it also terminates).

System Crate

Details of the operating principles of the Hytec System Crate, including the use of Branch Couplers, are given in the two documents “Hytec System Crate Philosophy” and “Configuring CAMAC System Controllers”. Briefly an Executive Controller (such as our MX–CTR–3) acts as the crate controller, and also arbitrates access to the crate ’N’ lines by one or more Program Source units that can take control of the crate, or system on a ’cycle–stealing’ basis, allowing the selected one to become System Master for one CAMAC cycle. The selected Program Source (such as a computer interface, located anywhere in the crate) puts out the whole command, consisting of data (if any) on the Read lines, sub–address and function code on the A and F lines, and address information (Branch, Crate and Station codes, see Table 1) on the Write lines.

This is the essence of the System Crate, putting data bi–directionally on the Read Lines and address on the Write Lines in short set–up period.

SC Mode

If the branch code is zero (SC Mode) the command is for a module in the System Crate itself, and the address information just consists of the binary value of N, and the Station number of the addressed module. The Executive Controller or Exec, selects the corresponding N line and starts a CAMAC cycle by asserting Busy, which is the signal for the Master Program Source to remove the (N) address code from the Write lines. The Exec then links Read and Write lines together, generates S1 and S2 timing strobes, and completes the cycle by making the Program Source end its access, and then removes Busy.

Branch Mode

If the Branch code is not zero (Branch Mode) the command is for a module in a crate on a Branch Highway, and the address information now consists of the Branch number, the Crate address on that Branch, and the Station number in that Crate (Table 1). The Exec selects the (even) N line corresponding to the Branch number (see Table 2) and the selected Branch Coupler starts to drive its Highway. Although Table 1 contains Serial codes as well as Parallel ones, we shall deal here only with the latter. Also note in that table two alternative modes of addressing: the Crate Address Register, CAR, used for multi–addressing some pre–selected set of crates, and the Stock register, SR, used for multi–addressing all on–line crates. In the same way Grant, G, overrides the A and F codes on the A and F lines, as well as all the N and C codes.

Branch Operation

The Branch Coupler links a remote CAMAC crate on a standard 66–twisted–pair Branch Highway in a transparent manner, that is, in a single composite System Crate CAMAC cycle. It is as though the register addressed in the remote crate were actually in the System Crate itself, although timing will naturally be a little slower: indeed, if a pair of our Differential Branch Extenders type DBE 6501 is used to produce a Branch Highway of a kilometre or more length, the timing will be a good deal slower. But it is still one single–addressed System Crate cycle, an example of the power of the System Crate addressing structure.

When the Branch Coupler is selected in Branch mode it automatically commences a Command mode operation on the Branch Highway. To do this it first issues BTA. When it receives the correct BTB replies it issues the T signal (see Table 1) onto the System Crate dataway 16 line, which allows the Exec to continue by issuing S1. This in turn causes the Coupler to remove BTA. On receipt of the correct final state of the BTB signals the Coupler removes T, allowing the Exec to issue and remove S2 and then go on to complete the System Crate cycle: at the same time the Coupler gates the Branch BX and BQ onto the SC dataway X and Q lines. The typical time for a complete cycle of this type for a near Branch crate is 1.2 microseconds for the type A crate controller the remote crate plus a System Crate overhead of comparable length, say a total of 2.4 microseconds. This compares very favourably with the time taken when a CAMAC module is used conventionally to drive a Branch Highway, which is typically double this length. The difference between the two methods increases still further when the time taken for a computer to perform its cycles is taken into account.

Demand Handling

The Branch Demand signal BD is made available at the rear panel after conditioning by the Enable/Disable logic within the Module Section, and also by a front–panel Enable/Disable switch which overrides the logic: BD is also disabled when the Coupler is switched off–line by another front–panel switch.

The normal response of a Program Source, be it a general computer interface or a special demand handler like our Interrupt Vector Generator IVG2404, is to perform a Grant GL or G operation to the appropriate Branch Coupler: in response to being selected in this way the Coupler performs a Graded–L operation on the Branch Highway. This is a multi–crate read operating, using the Stock Register to address all on–line crates, in which BG (Branch Grant) is set to 1 and all/any C, N, A, F codes are ignored. The corresponding R/W data, containing Branch GL bits, are gated onto the SC Read lines in the normal way.

Physical

The front panel carries the driving Hughes 132–way fixed socket, seven LEDs to indicate the state of the Stock Register, seven more for the Crate Address Register, plus two more to indicate BD Enabled and BD Present, and there are three switches: a Branch Initialise switch (only effective when Coupler is off–line), a BD Enable/Disable switch and a lever–lock On–Line/Off–Line switch.

Connections to the branch highway are given for convenience in Table 4.

The rear panel carries just three Lemo RA00 2500 sockets: the BH termination voltage monitor socket, the Branch Demand socket and an L socket: this last can be linked to the BD socket if required on a particular system, so that Branch Demands may be handled via the L–GL route rather than directly. In addition, there is a hole giving access to a potentiometer controlling the BH termination voltage, and the BR–CPR–4–1 also carries a lever–lock ’Module–even’/’Module–odd’ address switch.

Signal standards are in accordance with those specified in EUR 4600 or EUR 4100 (or their corresponding IEEE and IEC equivalents).