The timing chain is divided down as shown in Figure 4. The horizontal counter chain divides the frequency of the clock down to positions 1H, 2H, 4H…128H.
The vertical counter chain is identical to the horizontal chain except that it counts horizontal sync pulses rather than clock pulses. The divider chain also gives submultiples of vertical positions known as IV, 2V, 4V…128V, as shown in Figure 4.
The two counters are used extensively throughout the system as described in subsequent sections.
Object Module Functions
A functional block diagram of each object module is illustrated in Figure 5. Each object module consists of:
1)A pair of coordinate registers describing the position of the object.
2)Each object is described by a RAM pattern of m x n bits.
3)Each object can have various sizes, depending on the shifting rate controlled by the program.
The size and shifting rate relationship is tabulated as follows:
Shifting Rate |
Object Size on a 25-inch Screen |
280 nsec |
0.8" x 0.6"
|
560 nsec |
1.6" x 1.2"
|
1120 nsec |
3.2" x 2.4"
|
2240 nsec |
6.4" x 4.8"
|
4480 nsec |
12.8" x 9.6"
|
The object module operates as follows: The pair of coordinate registers specifies the location where the object is to be shifted out. A set of master counters and vertical and horizontal counters is available from the sync block to indicate where the electron beam is at a given instant. When the coordinate registers match the master counters, the object pattern is shifted out.
The size of the object can be controlled by controlling the shifting rate of each object. The resolution is controlled by the size of the pattern. A finer object can be painted by a bigger pattern.
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