268XA
Service Manual
2-12
Microcontroller
A Texas Instrument MSP430P337A mixed signal microcontroller is the heart of the DIO
PCA. The microcontroller, U4, features bi-directional digital ports, a built in UART and
internal timers for controlling operation. A quartz crystal operating at 32.8 kHz provides
the main clock signal for the microcontroller. This signal is internally multiplied to
3.6925 MHz for clocking of the microcontroller functions and is also divided down to
8 kHz (XBUF U4 Pin 97) providing a control signal for the debounce PLD; U3.
Internal to the microcontroller is a watchdog timer that is set to a 1 second interval.
Should the microcontroller become inoperative for a period of 1 second, the watchdog
timer will activate and perform a Power Up Clear (PUC) operation that resets all outputs
and restarts the microcontroller. C50 controls the duration of the reset signal.
During power up, U16 provides a reset pulse of approximately 2 seconds to insure that
the crystal oscillator (Y1) is given sufficient time to start. U16 also has undervoltage
detection such that if the supply voltage to pin 2 drops below 4.5 V, the output will reset.
Depressing S1 can manually reset the microcontroller. This applies a ground signal to the
reset (RST U4 pin 96) pin of the microcontroller.
U3 is an Atmel ATF750C Programmable Logic Device (PLD) and is configured as a
signal debouncer. The Totalizer signal is applied to U3 Pin 13 from the Totalizer Input
Protection Buffer circuit (U1 Pin 1 and U18. See Totalizer Input section for more
information).
Localized communication to the DIO PCA can be accomplished by connecting a RS-232
terminal to P3 or P4 and moving R35 (a zero ohm resistor) to position R36 (this redirects
the receive signal from the mainframe to the microcontroller to the RS-232 port). U2
(Maxim MAX232) accomplishes the bi-directional RS-232 communication. It uses a
single supply (+5 Vcc) and internally level shifts the signals to standard RS-232 levels.
Communication is controlled by the built in UART in the microcontroller (URXD U4 Pin
51 receive and UTXD U4 Pin 50 transmit) at a rate of 120k bps. Communication is
performed in 6 byte packets (bytes 0-4 contain command data while byte 5 is a
checksum) and is done in hexadecimal format. You will need a special software program
(Perl script) to communicate via P3 or P4 for debug purposes. Using “terminal.exe” or
“hyperterminal.exe” in windows will not work as the communication is in ASCII format.
U17 is simply an output buffer for driving the opto-isolated A/D power supply.
The MSP430P337A is a One Time Programmable (OTP) device and will be pre-
programmed by the supplier however should the need arise, it is possible to program a
blank device on board through the JTAG Programming Port P2. A serial-programming
adapter supplied by Texas Instruments must be used in order to program the device. R34
must be replaced with a zero ohm resistor so that the programming adapter can control
the clock of the microcontroller. After programming is complete, R34 is removed.
Data Input Threshold
The Digital Input Threshold circuit sets the input threshold level for the Digital Input
Buffers and the Totalizer Input. A fixed value voltage divider (R5, R6) and a unity gain
buffer amplifier (U1) are the main components in the circuit. The voltage from the
divider (approxi1.4 V dc) is then buffered by U1, which sets the input threshold.
Capacitor C8 filters the divider voltage at the input of U1.
Summary of Contents for 2680A
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Page 207: ...Replaceable Parts Parts Lists 7 7 13 2680A DIO alg100f eps Figure 7 3 DIO Module ...
Page 209: ...Replaceable Parts Parts Lists 7 7 15 2680A FAI alg102f eps Figure 7 4 FAI Module ...
Page 211: ...Replaceable Parts Parts Lists 7 7 17 2680A PAI alg103f eps Figure 7 5 PAI Module ...
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Page 215: ...8 3 8 Schematic Diagrams Figure 8 1 Backplane PCA 2680A 4001 ...
Page 216: ...268XA Service Manual 8 4 Figure 8 1 Backplane PCA cont 2680A 1001 ...
Page 217: ...8 5 8 Schematic Diagrams Figure 8 2 Controller System Power PCA 2680A 4004 ...
Page 223: ...8 11 8 Schematic Diagrams Figure 8 3 Digital I O PCA 2680A 4006 ...
Page 224: ...268XA Service Manual 8 12 Figure 8 3 Digital I O PCA cont 2680A 1006 1 of 3 ...
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Page 227: ...8 15 8 Schematic Diagrams Figure 8 4 Backplane Extender PCA 2680A 4009 ...
Page 228: ...268XA Service Manual 8 16 Figure 8 4 Backplane Extender PCA cont 2680A 1009 ...
Page 229: ...8 17 8 Schematic Diagrams Figure 8 5 Extender PCA 2680A 4010 ...
Page 230: ...268XA Service Manual 8 18 Figure 8 5 Extender PCA cont 2680A 3010 ...
Page 231: ...8 19 8 Schematic Diagrams Figure 8 6 A D Supply Assembly 2680A 4031 ...
Page 232: ...268XA Service Manual 8 20 Figure 8 6 A D Supply Assembly cont 2680 1031 ...
Page 233: ...8 21 8 Schematic Diagrams Figure 8 7 PCMCIA PCA 2680A 4041 ...
Page 234: ...268XA Service Manual 8 22 Figure 8 7 PCMCIA PCA cont 2686 1041 ...
Page 235: ...8 23 8 Schematic Diagrams Figure 8 8 Output PCA 2680A 4062 ...
Page 236: ...268XA Service Manual 8 24 Figure 8 8 Output PCA cont 2680A 1062 ...
Page 237: ...8 25 8 Schematic Diagrams Figure 8 9 A D PFE PCA 2640A 4003 ...
Page 238: ...268XA Service Manual 8 26 Figure 8 9 A D PFE PCA cont 1 of 6 ...
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Page 244: ...268XA Service Manual 8 32 Figure 8 10 A D FFE PCA 2645A 4003 ...
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Page 250: ...268XA Service Manual 8 38 Figure 8 10 A D FFE PCA cont 700p29_topress zip 2645A 1003 6 of 6 ...
Page 251: ...8 39 8 Schematic Diagrams Figure 8 11 Analog Input Connector PCA 2620A 4004A ...
Page 252: ...268XA Service Manual 8 40 2620A 1004 Figure 8 11 Analog Input Connector PCA cont ...
Page 253: ...8 41 8 Schematic Diagrams Figure 8 12 Display PCA 1 of 1 ...
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