HP 214B User Manual

Model 214B
SERVICE BLOCK A1·1
BURST BOARD A6
THEORY OF OPERATION
The Bur st Control essentially consists of a cou nter which is loaded with numbers from front panel thrumbwheel
sv,'itches. When a burst is started, pulses from the rate generator decrement the co unt er until it is empty.
Thi s condition (all zeroes) is detected and generates a BURST COMPLETE signal which disables the rate
generator.
The
following description divides the burst operation into four successive stages:
1.
Loading the Burst Counter
2. Start Burst
3. Zero Detection
4. Burst Complete
Loading the Burst Counter
When BURST mode is selected, the BURST ENABLE line goes high (0 V) and 'clears' U319 (via 0307, C306,
U313, U312), setting the 0 output low . A low on this outp ut then enables data to be loaded from the thumb -
wheel switches
into the counter.
As data is bei ng loaded, a comparator (U30 1, U302, U307, U308 ) checks for equiva lence between the
counter inputs and outputs . When equivalence is detected, input pin 11 of U312d goes high, and the LOAD
line (from output pin 13 of U312d) goes low thus preventing brther lo ading of the counter.
Throughout this load process, the high on the 0 output of U319 disables the repetition rate generator
(via
AND gate CR311 , CR312 and OR gate 0302, 0303) and therefore prevents the counter from counting .
Start Burst
When the START BURST signal is received, U319 is 'preset' (via NAND gate 0305, 0306) causing the 0
and
Q outputs to change state. The low on the Q output starts the repetition rate generator, and the counter
begins to count down from the preset number . The high on the 0 output of U319 ensures that the LOAD
li!1e remains disabled, thus preventing a re-Ioad of the counter (e.g. by th!..lmbwheel switch change) before
the end of the burst .
Zero Detection
Throughout the count-down process, all outputs of the cou nter are monitored by two 'zero detect'
configurations, one consisting of U309 and U311, and the other consisting of U309 and CR302 -> CR31O.
The significance
of the two configurations is explained in the following Burst Complete description.
Burst Complete
When the counter reaches the 'all zero' condition, the fast 'zero detect' circuit (U309, CR302 -+ CR310)
generates a BURST COMPLETE signal, which disables the repetition rate generator via OR gate 0302,
0303. This fast zero detection is achieved by using a 'hot carrier' diode for CR310, which monitors the
final zero state, C301, of the counter. Fast detection then ensures t~at the repetition rate generator is
switched off after the correct number of pulses have been output.
Appendix
Al -9
Scans by Artekmedia => 2009

HP 214B Specifications

General

Brand	HP
Model	214B
Category	Portable Generator
Language	English