The basic CAMAC specification (see Ref [1]) defines a single CAMAC operation as the activity which oc curs in response to a single CAMAC command. This activity may consist of the transfer of a single data word bet ween a CAMAC module and computer memory or the changing of the status of a module [for example, F (26), F (24)] or return of a value for Q as the result of a test made on the module, or any compatible set of the previously named activities. A block transfer is defined as a sequence of single CAMAC operations involving data which the user specifies by a command said to be of a higher level than one which specifies a single CAMAC operation. The higher level command contains all the information required for the specification of the desired sequence of single CAMAC command s and is interpreted by a channel which governs the activity on the CAMAC highway. Control information such as the readiness of the computer to participate in a data transfer, the state of the CAMAC Q line and the state of certain LAMs (Look-at-Me's) or special synchronizing signals must be made available to the channel. The use made of the control information by the channel defines the block-transfer mode. If a module is to influence the sequence of ope rations within a block transfer, then it must have the features required by the algorithm.