Electronic up-down conting system with directional discriminator

An electronic up-down counting apparatus arranged to respond to a pulse input representative of measurement information, the pulse input being in the form of two first pulse trains which have substantially identical repetition rates but are phase shifted relative to one another so as to indicate a direction of counting to be effected, said counting apparatus comprising:

• a pair of time delay circuit means, each of which is responsive to a respective one of the two first pulse trains and is operative to generate a respective second pulse train which corresponds but is slightly phase shifted with respect to the respective one of the two first pulse trains;
• a read only memory having at least four address input terminals, each of which is connected to a respective one of the first and second pulse trains, and at least first and second output terminals, said read only memory programmed to produce output signals on the output terminals in response to the first and second pulse trains, which output signals are representative of the pulse input and the direction of counting, said output signals including a plurality of first output pulses on the first output terminal indicative of movement in a first direction of counting and a plurality of second output pulses on the second output terminal indicative of movement in a second direction of counting, opposed to the first direction of counting;
• and
• up-down counting means for maintaining a count, incrementing the count in response to the first output pulses, and decrementing the count in response to the second output pulses, said counting means including an incrementing terminal connected to the first output terminal of the read only memory and a decrementing terminal connected to the second output terminal of the read only memory.