Novametrix Medical Systems 515 Service Manual page 18

Theory of Operation:Analog Board #2288
Service Manual: Model
1.4
1.4.1
A0-B7 0
X X
X
Static addr bus enable (1/2 1CG2(
A0-B7
0
X
X X
Static data bus enable (ICG 19 enl
A0-B7
0
0
X
1 PWR
Static WR line
A8-AB
0
X X
X CSGAN
Gain/offs DAC chip select
AC-AF
0
X X
X UPOFF
Gain/offs DAC output update enb
B0-B1
0 X X X CSLED
(0-logic low; 1-logic high; X-don'tcare)
LED drive DAC chip select
The Y4, Y5, Y6 outputs of ICG 15 that correspond to I/O addresses for
LED drive DAC, the gain/offset DAC and the ADC are NANDed at ICG6 ]
1, 2, 13, the output is then inverted by ICG7 pin 11 to produce a signal
controls the enable pins of ICG 19 and half of ICG20 (this allows data from
address and data busses to be transferred). This signal is also ORed with
CPU's WR line and inverted E line at ICG9 to produce the PWR (static
line) when writing data to the front end. The direction of the data flow is (
trolled by connecting the CPU's RD line to the DIR line of ICG 19. When
RD line is low (CPU read cycles) the data flow is from the B to A pin?
ICG 19, when RD is high data flows in the opposite direction.
Analog Board #2288
The drive circuitry for the REDLED and IRLED along with the detec
and decoding circuitry is found on the 2288 analog board. The processor c
municates with the analog board through a 40 conductor ribbon cable locate
El. All the timing signals and power lines are run through the ribbon cabL
well. The sensor connects to the analog board at J405 and is run to the f
panel connector by a cable assembly.
Probe Detection
The monitor recognizes that a probe is connected by monitoring pins 5
6 of J405 (REDLED and IRLED cathodes). A dual comparator IC23 has
positive inputs tied to 1/2 VLED (=2.4 VDC). The negative inputs of IC23
tied to the REDLED cathode (pin 2) by R64, and to the IRLED cathode
6) by R65. Resistors R66 and R67 hold the negative inputs low when no pi
is connected. When the probe is connected both pins 2 and 6 are brought 1
which brings the outputs of both comparators low. When the probe
disconnected pins 2 and 6 are at ground potential and the outputs are high
to pull-up resistors R48 and R47. This will signal the processor to flas
"CONNECT
87XX
PROBE"
message on the display.
If either of the LEDs malfunctions and causes the output of a comparatc
remain high while the other goes low then an error message will be displa;
A malfunction with the IRLED will flash
"PROBE ERROR-04",
a malfunc
with the REDLED will flash
"PROBE ERROR-02".
The point of pins 3 and :
IC23 is also monitored by the A/D converter ICl 1, if IC24 were to malfunc
or if El were to blow then
"MONITOR ERROR-0001"
would be displayed.