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Programming Issues
1
Parallel (Printer) Interface
1-14
The CD2401 supports DMA operations to local memory. Because the
CD2401 does not support a retry operation necessary to break VMEbus
lockup conditions, the CD2401 DMA controllers should not be
programmed to access the VMEbus. The hardware does not restrict the
CD2401 to onboard DRAM.
The PCCchip2 ASIC provides an 8-bit bidirectional parallel port. All eight
bits of the port must be either inputs or outputs (no individual selection).
In addition to the 8 bits of data, there are two control pins and five status
pins. Each of the status pins can generate an interrupt to the MPU in any
of the following programmable conditions: high level, low level,
high-to-low transition, or low-to-high transition. This port may be used as
a Centronics-compatible parallel printer port or as a general parallel I/O
port.
When used as a parallel printer port, the five status pins function as: Printer
Acknowledge (ACK), Printer Fault (FAULT ), Printer Busy (BSY),
Printer Select (SELECT), and Printer Paper Error (PE), while the control
pins act as Printer Strobe (STROBE ), and Input Prime (INP ).
The PCCchip2 provides an auto-strobe feature similar to that of the
MVME147 PCC. In auto-strobe mode, after a write to the Printer Data
Register, the PCCchip2 automatically asserts the STROBE pin for a
selected time specified by the Printer Fast Strobe control bit. In manual
mode, the Printer Strobe control bit directly controls the state of the
STROBE pin.
Refer to
Chapter 3, PCCchip2
Refer to
Appendix C, Related Documentation
port interface connections.
for detailed programming information.
for drawings of the printer
Computer Group Literature Center Web Site
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