Tektronix 2246 1Y, Service Manual

Page: 54 / 433

Theory of Operation—2246 1Y and 2246 Mod A Service
DIO: Data 10 pin. This pin is tied to the
Measurement Processor MB DATA line. Data
to be clocked into the control register is pre­
sented here, and status data can be read
out on this pin when the RD input is low
(tri-state output). See Table 3-7.
TDI: Trigger data input pin. When A3=A2=1,
data on this pin is sent to the DIO pin (when
RD is low ).
RD: Read enable input (active low). Bringing
this pin low causes internal status data
(selected with A3-A0) to be presented on
the DIO pin for transfer to the Measurement
Processor.
WR: Write enable input (active low). A
negative-going pulse on this pin performs
actions described in the Table 3-7.
SOUT: Strobe output pin (active low ). When
A3, A2, A1_;_and AO = 1111, SOUT goes low
when the WR pin is pulled low. Otherwise,
SOUT is always high.
A3, A2, A1, AO: Address inputs. The
ADDR0-ADDR3 selection bits are latched
from the Measurement Processor address
bus by U2512, Diagram 8.
A GATE: A Sweep Gate input (active low).
B GATE: B Sweep Gate input (active low).
TC: Timing clock input.
LFC: Low-frequency clock input. A signal
derived from the calibrator circuit is used for
skewing the chop-clock phase.
ROR: Readout request input (active low). A
low causes the CH 1 EN, CH 2 EN, CH 3 EN,
CH 4 EN, HD1, HDO, and TS outputs to all go
low, and allows the ROB input to have com -
plete control of the BLANK output. If ROB is
low when ROR goes low, then the internal
timing will be such that the BLANK output will
go high quickly enough to blank the display
before switching transients can be shown on
screen (see the detailed description of the
readout interface).
ROB : Readout blank input (active low ). Dur-
ing readout active time (ROR=low), the ROB
input is inverted and sent to the BLANK
output.
OSC OUT: The external holdoff oscillator
output drives this pin. A falling edge causes
the internal holdoff counter to increment.
OSC RST: Oscillator reset output. Internal
logic causes this output to go high to dis­
charge the external holdoff oscillator timing
capacitor at the end of holdoff (see detailed
description of the holdoff tim er operation).
CH 1 EN: Channel 1 enable output (active
high).
CH 2 EN: Channel 2 enable output (active
high).
CH 3 EN: Channel 3 enable output (active
high).
CH 4 EN: Channel 4 enable output (active
high).
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