Printer system having parity checking of print hammers using software control

摘要

A printer control system for a belt printer has an arrangement for checking print hammer operating circuits by comparing a real time actual parity of the circuits with a precalculated expected parity. Prior to printing, a microprocessor calculates expected parity bytes for each subscan for storage in a storage device along with the print position fire data used for selecting the operating circuits to be activated in the related subscans. An actual parity byte is generated on a real time basis by ODD/EVEN parity circuits associated with groups of operating circuits for comparison with a composite parity byte generated each subscan by the microprocessor. The composite parity byte is generated by combining the expected parity bytes from the storage device for several successive subscans. The composite parity byte is updated each subscan by a process of subtracting the initial expected parity byte and adding a new subscan expected parity byte. Comparison is made when all the activating circuits are in stable condition.