289 
For instance, some of the switch functions can be controlled from the video 
terminal and this terminal can also display the coordinates instead of using 
console counters. 
Some advanced systems have additional computer control of the observed optical 
image, affecting the magnification and rotation of viewing fields. In the 
context of this paper this optical control is irrelevant and is disregarded in 
Figure 2. 
Distributed Processing 
The concept of distributed data processing is based on the use of a supporting 
computing power of microprocessors which in effect relieves the function of 
the computer. The processor is preprogrammed to perform certain standard or 
utility functions via firmware. It can then be equipped merely with 'read 
only' memory, while variable parameters are supplied from the computer. 
Figure 3 renders an example of a two-level distribution, as typical for the 
HAI US-2 analytical plotter. The processor eliminates the real-time 
positioning function from the computer control. Coordinate registers are 
attached to the processor which then receives the X, Y, Z input from the 
operator. The processor assumes full responsibility of real-time position 
calculations and servo control. The switch functions are also directed 
through the processor. Another example in Figure 4 illustrates a three-level 
  
  
ANALYTICAL PLOTTER 
SERVO | 
CONTROL 
COMPUTER PHOTO STAGES 
PROCESSOR | 
- | REGISTERS | 
COUNTERS SWITCHES INPUT XYZ OPTICS 
VIDEO ] 
TERMINAL 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
M 
Fat] 
  
  
  
  
  
  
  
  
  
  
Ï l 
| OPERATOR 
  
  
  
Fig. 3 Two-level distributed processing 
  
  
ANALYTICAL: BLOTTER 
SERVO CONTROL | 
COMPUTER I 
PROCESSOR 1 PHOTO STAGES 
| REGISTERS | 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
I—] PROCESSOR 2 1 
T ' VIDEO TS SWITCHES INPUT XYZ OPTICS 
  
  
  
A 
  
  
  
  
  
Ee ERU il SCREEN 
COUNTERS 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
| OPERATOR 
  
Fig. 4 Three-level distributed processing