IBM 6400 Series, Maintenance Manual

Page: 49 / 428

49
Principles of Operation
“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 50), which has access to
the VX through the “Cajun” Bus Interface.
“Cajun” Bus Interface The “Cajun” bus interfaces 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 an IEEE 1284 Level 2 host
♦
Interface to RS–232E serial host
♦
Interface to RS–422 serial host
All the circuitry required for these host types is provided on the CMX 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 are DIP-socketed
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/
m
s slew rate for all outputs.