Printronix 108525-001, Maintenance Manual

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2-27 P6040/P6080 Principles of Operation
2-6. Logic C3 PCBA
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continued
j. Mechanism Interface
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Many signals from the printer are received by the logic C3 card through the J2 connector. The most
important signal is MPU, since this is the signal which the software uses to synchronize the data to
be printed with the mechanism. The MPU pulse train generates interrupts with every pulse, and
these interrupts are used by software to time the transfer of data to the hammer driver card. The
signal NRESYNC is detected by using a one-shot circuit. The NRESYNC signal also generates
an interrupt. The time of the retriggerable one-shot is varied when using a P6040 or a P6080 by
the addition of the jumper E20-E21.
The NRESYNC is detected by the software reading the status port address 40082. Since the MPU
and NRESYNC interrupts are at the same vector GPI6 of the 68901, the status port is used for
differentiation between the two interrupt sources.
k. NRESYNC Generation
As stated above, on the logic C3 card the NRESYNC signal is generated by the use of the one-
shot circuit that is jumper selectable for either of the P6040 or a P6080. For the P6040 the one-
shot timer will trigger if the MPU pulse train is slower than a 720 m s period. For the P6080, the
RESYNC signal is generated when the MPU pulse train is slower than a 550 m s period. Note that
the jumper E20-E21 selects the P6080 NRESYNC timing when installed. NRESYNC is treated
as an interrupt to the processor, handled through the 68901 MFP.
l. Hammer Load Circuit
The hammer load circuit unloads the dot image buffer after the software writes to an address enaĆ
bling the circuit. The circuit operates entirely from hardware, except for the starting address of the
dot image buffer. The circuit will transfer dots to the hammer driver card at one of two rates, 1
MHz or 3.33 MHz. The jumpers which change the hammer load rate are called E38, E39 and E40.
With E38 and E39 shorted the rate to transfer to the hammer driver card is 3.33 MHz, while E39
and E40 shorted, the data transfer rate is restricted to 1MHz (P6080 hammer driver PCBA comĆ
patibility).
When active this circuit stops the processor by not returning the DTACK signal until the loading of
the hammers is complete. This means that this circuit will tie up the bus for 44 m s and 66 m s respecĆ
tively when running at 1MHz transfer rates in a P6040 or P6080.
m. Hammer Reset Timer
This circuit is controlled by a one-shot timer. The pulse train to the one-shot is controlled by
software hammer reset (NSWHRS) and the pulsed train is driven by MPU. The hammer reset
timer is set for approximately 384 m s, so that 384 m s after the MPU pulse, the hammers are reset.
This is true for the P6040 configuration, but in the P6080 configuration, the hammer reset timer
card is added as a piggyback card on the PCBA.
The hammer reset timer PCBA, p/n 104363, is located at 4A. When this card is in place, its actions
override that of the one-shot HRS signal generated on the logic C3 card.
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