Integra CROMA24 - Manual (Page 36)

36 Theory of Operation
Croma24 Service Manual
The direction that the Carrier Assembly is moving is known based
upon the state of one detector’s output and the direction of the
transition of the other detector’s output.
A hardware counter in the gate array increments as the Carrier
Assembly moves left and decrements as the Carrier Assembly moves
right. The hardware counter is only eight bits wide, so it cannot
store a value large enough to represent an absolute Carrier Assembly
position. Instead, it is read during the servo interrupt and its value
compared with that from the previous interrupt. This difference is
used to update the absolute position value in the software.
Interface Circuits: Serial & Parallel
Figure 2-9. Interface Circuits.
Data from the host computer is received either through the
Centronics parallel port or the serial port (on the GA/CAD or GA
versions only). The gate array provides the control signals for DMA
transfers from the serial port to DRAM.
The serial port is designed primarily to interface to a Macintosh
printer port. It has an eight pin Mini-DIN connector. The data
(TXD, RXD) signals meet RS-422 electrical specifications, and the
control signal (DTRCLK) meets the RS-423 electrical specifications.
The control signal can be configured as a 1 MHz clock for high speed
serial communications with a Macintosh.
The serial port is compatible with RS-422 devices when an appropri-
ate adapter cable is used. This cable is available from ENCAD.