Interface for mailing system peripheral devices

Claim 1

An interface between a weighing cell providing weight information in the form of coded digits representative of arbitrary weight units and an OCIA type port for a data processing system, comprising: (a) data input means connected to a serial data input line and to an associated input clock line, both from said OCIA type port, for receiving serial data input words shifted individually into said input means from said serial data input line by series of clock pulses of a predetermined length on said input clock line and for converting said serial data input words to parallel input words individually; (b) data output means connected to a serial data output line and to an associated output clock line, both to said OCIA port, for receiving parallel data output words individually and for shifting said data output words individually out on said output line in a serial format by means of series of clock pulses of a predetermined length received on said output clock line, said output means further comprising: (1) a parallel loaded shift register, said shift register having a first stage, a second stage and a further plurality of stages, said stages each having an input and an output, said first stage's input being hard-wired to a predetermined logic level indicative of an inactive state of said output means, said second stage's input being hard-wired to the opposite logic level to said predetermined level indicative of a data available state of said output means, and the inputs of said plurality of stages receiving said individual parallel data output words, and said shift register having said first stage output connected to said data output line and a clock input connected to said output clock line and to an interface control means for receiving clock signals to shift data in said shift register, whereby when said individual parallel data output word is loaded into said shift register and shifted once said indicative opposite logic level is placed on said output line to signal said port on said output line that data is available, said port responding to said indicative opposite logic level by providing series of clock pulses to shift out the contents of said first stage (equal to said indicative opposite logic level) and said individual parallel data output word to said port, and; (2) means responsive to said series of clock pulses for signalling to said interface control means when said output means has transferred said individual output data word to said port and for then initiating a load operation to reset said first stage to said predetermined logic level; (c) said interface control means being connected to said data input means and said data output means, and connected to said weighing cell for (1) receiving said parallel input words individually, sequences of said words defining a plurality of types of messages; (2) in response to one particular type of said messages, receiving weight information from said weighing cell; and, (3) transferring said parallel data output words representative of said weight information to said output means.