TIBPSG507AC Datasheet, PDF (12/19 Pages) Texas Instruments – 13 × 80 × 8 PROGRAMMABLE SEQUENCE GENERATOR

TIBPSG507AC
13 × 80 × 8 PROGRAMMABLE SEQUENCE GENERATOR
SRPS002D – D3029, MAY 1987 – REVISED NOVEMBER 1995
PRINCIPLES OF OPERATION
PSG design theory
Most state machine and waveform generator designs can be simplified with the PSG by referencing all or part
of each sequence to a binary count. The internal state registers can then be used to keep track of which binary
count sequence is in operation, to store input data and keep track of internally generated status bits, or as output
registers when connected to a nonregistered output cell. State registers can also be used to expand the binary
counter when a larger counter is needed.
Through the use of the binary counter, the number of product lines and state registers required for a design is
usually reduced. In addition, the designer does not have to be concerned about generating wait states where
the outputs are unaffected because these can be timed from the binary counter. For detailed information and
examples using this design concept, see A Designer’s Guide to the TIBPSG507 applications report.
OR term loading
As shown in Figure 3 and by the f_max calculation, f_max is affected by the number of terms connected to each OR
array line. Theoretically, f_max is calculated as:
) ^{fmax =} tsu
1
tpd CLK to Q
Since the setup time (input or feedback to S/R↓) varies with the number of terms connected to each OR array
line, (due to capacitance loading) f_max will also vary. Figure 3 illustrates the relationship between the number
of terms connected per OR line and the setup time.
Use Figure 3 to determine the worst-case setup time for a particular application. Identify the OR array line with
the maximum number of terms connected. Count the number of terms and use the graph to determine the setup
time.
WORST-CASE SETUP TIME
(input or feedback to SR↓)
vs
”OR” TERM LOAD
20
VCC = 4.75 V
19 ^{TA = 75°C}
18
17
16
15
14
13
12
11
10
0
20
40
60
80
Maximum Number of OR Terms Connected
Figure 3
12
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