Data Controller
267
Control Panel Interface
The VX operator panel interface consists of five lines: serial clock, serial data,
and three select lines. It is the VX that handles all parallel-to-serial (and vice
versa) conversion to and from the panel, as well as any special timing needed
when toggling select lines, etc.
“Dot Plucking” And Adjacent Dot Checking
“Dot Plucking” is a specialized DMA function that removes dot data from a dot
image buffer in DRAM in a programmable manner, serializes it, and sends it
to the hammer bank. This function is actually controlled by the EC (see page
268), which has access to the VX through the “Cajun” Bus Interface.
“Cajun” Bus Interface
The “Cajun” bus connects the DC, the EC, and the expansion port. The EC
uses this bus to access DC resources, including the semaphore registers.
(The semaphore registers are the primary communications path between the
EC and DC.)
Ports
The VX ASIC controls the following I/O functions:
• Interface to IEEE® 1284 Level 2 host
• Interface to RS-232-E serial host
• Interface to RS-422-B serial host
All the circuitry required for these types of hosts is provided on the controller
board, except for the drivers themselves, ESD protection, and terminations.
Host I/O Drivers And Termination
Beyond the 030 processor and VX ASIC, additional support circuitry
completes the serial and parallel interfaces. These circuits include:
• RS-232 drivers and receivers. These circuits use internal charge pumps
to eliminate the need for
±12V power.
• RS-422 differential drivers and receivers
• Parallel port pull-up and pull-down terminating resistors in DIP
configuration for easy removal and installation.
All interface ICs and terminations have the following characteristics:
• Provide ESD protection to 15KV for all inputs.
• Less than 0.05V common mode ripple, measured at the power and
ground of the interface ICs.
• Less than 0.02V common mode ripple, measured between chassis
ground and the ground pins of the interface ICs.
• Greater than 200V/µs slew rate for all outputs.
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