Abstract: A FIR digital filter comprises a plurality of cascaded subfilters all operable at the same sampling rate. At least one of the subfilters has a z-transform transfer function defined by a partially factorized, n.sup.th -order polynomial in z.sup.-1, where n>2 whose co-efficients are quantized. A process for deriving the z-transform transfer function of the filter is described.

Abstract: The present invention provides for a communication bus (52) and controller (54) which can control communication in more than one communication mode on a TDM bus by inhibiting or interrupting communication in a first mode during communication in a second mode. The bus (52) includes a allocate channel for controlling the bandwidth allocation of the bus amongst the different communication modes.

Abstract: A plurality of portable tokens are issued e.g. for authenticating instructions within an electronic banking network. Each token requires entry of a respective password in order to operate and becomes locked if a number of incorrect password entries are made. Each token also stores a respective cryptographic key and a random number generator. In order to unlock a locked token it outputs a random number and also encrypts that number under its respective key but does not output the result of the encryption. The random number is transmitted by the user to a central authority which stores the keys for all tokens. The authority encrypts that number under the respective key and returns the result of the encryption to the user of the token. The returned number is entered into the token and if it agrees with the result of the internal encryption the token is unlocked.