Abstract: a system of arbitration for access to a common memory by two asynchronous microprocessors without excluding either microprocessor for more than a predetermined, limited period of time. Two asynchronous microprocessors are connected to a common memory through an arbitration controller with a connection to transmit a "not ready" signal to one microprocessor requesting access when the other is in the process of accessing the common memory. A flip flop is connected to generate a predetermined signal output when a microprocessor requires access to the common memory, and this predetermined signal initiates a shift register to provide the internal timing of the asynchronous microprocessor requiring such access to bring it into synchronism with the clock controlling the internal cycle of the common memory.

Abstract: A printer control apparatus provides a control circuit arrangement which enables flight timing to be performed during printing. Basically, the invention achieves this by providing flight time control means activated by a print hammer operation signal. Preferably the control temporarily inhibits the continuation of print hammer operation. Preferably the control inhibits print hammer operation subsequent to a selected print hammer by inhibiting the comparisons of print line and type element data contained in storage devices of the print control. Inhibiting may be for a fixed interval based on an average of the flight times of all the hammers. Alternatively the inhibiting interval may be varied according to the individual flight times of the hammers. In order to avoid slowing the print speed excessively, only one hammer is timed during printing of one line.

Abstract: A printer control system uses two microprocessors and a print control for operating a plurality of print hammers in synchronism with a revolving type carrier. One microprocessor is a mechanical control processor, the print hammers are operated by a self timed print control system and the other microprocessor is a print control processor that communicates with a host system for receiving print and control data used by the print control and the mechanical control processor for operating the printer. The mechanical control processor monitors a speed selection device such as an operator panel with speed control keys and operates controls for operating drive means for moving the type carrier at selected speeds. The print control processor supplies speed control data from a diskette to the mechanical control processor for control the type carrier speed.

Abstract: A hammer timing control system for the print hammers of a line printer uses a plurality of read/write RAMs in place of individual fire control circuits for controlling the firing periods of the hammers. A delay value RAM stores individual delay values to be interposed before each hammer is fired, and a terminate fire RAM stores a delay value to be interposed before the firing of a hammer is terminated. The hammers are turned on and turned off by signals incrementally clocked out from two pairs of RAMs which store each hammer address at memory locations corresponding to the hammer's assigned delay values.

Abstract: A fault protection system for impression devices of a printer detects fault current in the impression devices during non-print operation, checks the impression devices individually to determine the location of the fault and then disconnects the impression devices from the power supply. The fault protection system also includes means for recording the fault location data in a storage means which can be called out for later use in repairing the impression devices.

Abstract: A control system for a band printer uses a correction memory which stores address correction values for resetting the start addresses of the address registers which operate to scan the band image and print line buffers. The correction memory is programmable to store different sets of address correction values when type bands having different size character sets and/or pitch are interchanged.

Abstract: A hammer timing control system for a line printer has a register for storing a digital delay value related to the actual flight time of a controlled print hammer. A delay counter activated by an initiate fire pulse counts timing pulses until the count equals the delay value in the register. A comparator generates a fire signal when the count equals the delay value in the register. The counter continues counting pulses to a second count whereupon the fire signal is terminated. The second count is either decoded or compared with a predetermined quantity in a second register to terminate the fire signal. The counter may also be an up/down counter which counts up to delay and down to terminate the fire signal. Delay values can be stored in an external memory device such as a magnetic disk for transfer to the individual registers for each of the print hammers.

Abstract: The control system for a line printer includes compensation circuit means for electronically changing the timing of the reference or home pulse to compensate for changes in the speed of the type characters on a continuous type carrier. The compensation circuit includes a storage register, a counter and a comparison circuit for comparing the content of the storage register and the counter. The counter when activated by a reference pulse generated from a reference mark on the moving type carrier counts subscan pulses generated from timing marks moving with the type characters. The storage register, which is programmable, stores different numeric values dependent on the speed of the type carrier representing different numbers of subscan pulses to be counted by the counter means. The comparator circuit compares the numeric value in the register with the count registered in the counting means.

Abstract: A hammer limit control for an on-the-fly line printer comprises a counter which counts compare signals from a compare circuit which detects coincidences of print data and type position data in synchronism with the motion of an endless type carrier. The counter maintains a running count of the number of compare signals for a control interval having a duration which is a function of the printing interval of a print line cycle. A hammer on storage device stores a plurality of compare counts registered by the counter at the end of each of a plurality of control intervals. An adder adds the running count registered in the counter to the total count stored in the storage means and stores the total sum in a hammer on register. When the total sum in the hammer on register equals a maximum number, a limit comparator generates a control signal which inhibits further comparisons by the compare circuit.