 SEC-PC USER MANUAL |
 |
|
|
|
| FISCHER COMPUTER
SYSTEMS - 445 Bay Street Angwin, California - 94508 Phone:(707) 965-2414 Fax:(707) 965-3687 Sales:(800) 362-8998 ©1986, Fischer Computer Systems | |
| | Home | | E-mail | | People | | SEC-PCI | | SEC-232m | | |
SEC-PC USER MANUAL |
|
|
|
|
| FISCHER COMPUTER
SYSTEMS - 445 Bay Street Angwin, California - 94508 Phone:(707) 965-2414 Fax:(707) 965-3687 Sales:(800) 362-8998 ©1986, Fischer Computer Systems | |
| | Home | | E-mail | | People | | SEC-PCI | | SEC-232m | | |
Designed for the IBM PC and compatible computers.
I/O mapped. Uses four consecutive ports, switch-selectable.
Can be programmed in any high level language that supports IN and OUT operations
1.75 amp maximum from +5 volt supply.
Two input transition per microsecond. Input stage has logic to detect rate errors. A count occurs on each state change of the input pair; thus there will be four times as many counts as complete cycles of the input.
Six decimal digits standard, optional 24 bit binary for each of the three
counters.
Interlocking logic and holding registers prevent erroneous reading
of a counter in transition.
A pair of quadrature-encoded TTL-level signals for each of the three counters.
Debounced and latched input for one single-pole, double-throw switch. Output may be jumpered to an interrupt.
Eight TTL signals.
Eight LSTTL outputs.
Four LED drivers.
A socket for 2716/2732 ROM or 6116 RAM is provided. The data in the ROM or RAM is read and written through an I/O port. This gives the user a known place to store either temporary or permanent information.
A fifty pin 'D' style connector is used. The mating connector and hood is provided with the SEC-PC.
Fischer Computer Systems guarantees this product to be free of defects in parts and workmanship for a period of one year from the date of purchase, limited to repair or replacement of the product when returned with transportation charges prepaid by customer and accompanied by a statement of the problem. This warranty does not apply to defects arising from misuse, accident,or customer modification.
Set the device port address with the switches at location U2 at the top of the board. To use the standard address of 816 (330 hex) set the top two switches OFF, the next two ON, the next two OFF, and the bottom two ON.To use some other address, express the number in binary, discard the two least significant bits, and set the remaining eight bits in the switches. The most significant bit, A9, goes in the bottom switch, SW8, with the rest in order. Set each switch ON for a one, OFF for a zero.
Determine whether an interrupt is to be used. If so, install a jumper to the desired interrupt line. The jumper area "INT" has the center column of pins bussed together and driven by the driver on the board. The left column of pins goes to inter-rupt levels IRQ3, 4, and 5 (top to bottom), while the right column of pins goes to interrupt levels IRQ7, 6, and 2. In general, an application where the board is programmed in a higher level language will not use interrupts and will omit the jumper.
Select any available full-length expansion slot in your computer, and install the SEC-PC there (with the power off, of course). Secure the board to the rear frame with the machine screw obtained when removing the previous board or blank panel.
A single fifty pin 'D' style connector is used for all signals to and from the board. Refer to the following page for a pinout diagram. If possible, dress the switch and encoder inputs away from the parallel port cabling. Use the grounds liberally, both as shielding and to provide a low impedance path from the encoders.
Each encoder input is an A,B signal pair. The A and B designations are arbitrary and may be reversed to change the direction of counting. Refer to the 'HINTS' section for some suggestions on grounding.
Each LED is driven in its own current loop. The anode goes to one of the 'Return' points and the cathode goes to the 'LED-n' driver output.
For electrical properties of the parallel input and output ports, refer to a TTL data book for 74LS241 and 74LS373 parts. Note specifically the current limitations of the outputs, and that the states of unconnected inputs cannot be guaranteed.
The following table gives pin numbers for the DB-50 connector as viewed from the rear of the computer. Pin 1 is at the top and to the viewer's left.
1. Switch Common 34. +5 volts 2. Switch NC 18. Switch NO 35. +5 volts 3. Encoder ZB 19. Encoder ZA 36. +5 volts 4. Encoder XA 20. Encoder XB 37. Ground 5. Encoder YA 21. Encoder YB 38. Ground 6. PO-6 22. PO-7 39. Ground 7. PO-4 23. PO-5 40. Ground 8. PO-0 24. PO-3 41. Ground 9. PO-2 25. PO-1 42. Ground 10. LED-4 26. Return 43. Ground 11. LED-6 27. Return 44. Ground 12. LED-3 28. Return 45. Ground 13. LED-5 29. Return 46. Ground 14. PI-4 30. PI-6 47. Ground 15. PI-1 31. PI-7 48. Ground 16. PI-3 32. PI-5 49. Ground 17. PI-2 33. PI-0 50. Ground
Consider the case of an operator at a digitizing table equipped with a cursor and a pushbutton. A data collection operation might have the following parts:
The SEC-PC board accepts inputs from three TTL-output quadrature encoders and monitors state changes on those inputs. The board is a bus slave and has no data transfer (DMA) logic.
The board contains three up-down counters named X, Y, and Z. Each counter
has six decimal digits for a maximum count of 999,999. (See 'BINARY OPTION',
below.) The three input stages accept quadrature signals from the encoders.
Counting
occurs on each of the four state changes of the input pairs. Therefore an
encoder with 1000 cycles per revolution will produce 4000 counts per revolution.
Rate error logic detects double state changes on the inputs.
There is an 18
digit register into which the counters are copied for reading.
A command
from the program copies all the counters simultaneously. Interlocking logic
insures that this transfer is made at a time when the counters are not in
transition. The program reads the three values from the holding register a digit
at a time, most significant digit first.
An input for an operator's switch, intended to mark data points to be recorded, is debounced and latched as 'FLAG', but has no effect on the counters. FLAG may be jumpered to cause an interrupt, or may be polled by the applications program. There are four LED drivers intended for feedback to the operator. For 'click' feedback a small speaker can be substituted for one LED.
Programming the shaft encoder counter board is done through four I/O ports.
The control port, 'C', has a standard value of 816 (330 hex, 1460 octal), but
may be any value that is evenly divisible by four. Address selection is done
using switches at location U2 with the top switch matching A2 and the bottom one
matching A9.
All programmed communication with the SEC board is done
with the following four OUT and four IN commands.
IN C Read Status/Data D7: Switch Flag when status, zero when data D6: Error Flag when status, zero when data D5: Always zero D4: Always zero D3: BCD number when data, one when status D2: BCD number when data, one when status D1: BCD number when data, one when status D0: BCD number when data, one when status IN C+1 Read Parallel Input Port IN C+2 Read RAM/ROM IN C+3 Clear Flag (read all ones) OUT C Write Synchronized Output Port D0=0: Clear counters and command register D0=1: Copy counters to holding register OUT C+1 Write Parallel Output Port OUT C+2 Write RAM OUT C+3 Write Command Register D7: Interrupt ENABLE D6: LED 6 D5: LED 5 D4: LED 4 D3: LED 3 D2: (reserved) D1,0 Channel Select 1,1 = Z 1,0 = Y 0,1 = X 0,0 = Status
An internal pointer is used for data and ROM accesses. This pointer is cleared to zero by any write to the command register and is incremented by data reads (left to right) and by RAM/ROM accesses.
The following two pages offer some rudimentary programming examples, the first in AT&T GW-BASIC and the second in Microsoft C. Both are tested programs that simply read the counters and type the values on the console. The following basic program was written for DECIMAL counters ONLY!
10 REM EXAMPLE IN AT&T GW-BASIC 20 REM 30 DIM X$(6),Y$(6),Z$(6) 40 C=816 : P=C+3 : REM DEFINE PORTS 50 X=1: Y=2: Z=3 : REM DEFINE COUNTERS 60 S1=1:S2=1:S3=1: REM SCALE FACTORS 70 O1=0:O2=0:O3=0: REM AXIS OFFSETS 80 PRINT TAB(25),"SEC-PC BOARD DEMO" 90 PRINT : PRINT 100 INPUT "PRESS 'RETURN' WHEN CURSOR IS OVER REFERENCE",J$ 110 PRINT "THANKS." 115 PRINT "PRESS DIGITIZER BUTTON TO DIGITIZE, BREAK TO EXIT":PRINT 120 OUT C,0 :REM CLEAR COUNTERS, RATE ERROR FLIP-FLOP 130 REM 140 REM MAIN LOOP 150 J=INP(P) :REM CLEAR SWITCH FLAG 155 OUT P,0 :REM SELECT STATUS 160 REM WAIT FOR OPERATOR SWITCH 170 IF INP(C)<128 THEN GOTO 170 180 OUT C,1 :REM COPY TO HOLDING REGISTER 190 IF INP(C)>191 THEN GOTO 340 200 OUT P,X 205 X$="" 210 FOR I=1 TO 6: X$ = X$ + CHR$(INP(C)+48) : NEXT I 220 OUT P,Y 225 Y$="" 230 FOR I=1 TO 6: Y$ = Y$ + CHR$(INP(C)+48) : NEXT I 240 OUT P,Z 245 Z$="" 250 FOR I=1 TO 6: Z$ = Z$ + CHR$(INP(C)+48) : NEXT I 260 REM CONVERT STRINGS TO NUMBERS, CHECK MINUS, SCALE, OFFSET 270 X1=VAL(X$): IF X1>7E5 THEN X1=X1-1E6 275 X2=S1*X1+O1 280 Y1=VAL(Y$): IF Y1>7E5 THEN Y1=Y1-1E6 285 Y2=S2*Y1+O2 290 Z1=VAL(Z$): IF Z1>9E5 THEN Z1=Z1-1E6 295 Z2=S3*Z1+O3 300 N=N+1 310 PRINT "DATA POINT";N; 320 PRINT TAB(20);"X=";X2;TAB(35);"Y=";Y2;TAB(50);"Z=";Z2 330 GOTO 150 340 PRINT "***THERE HAS BEEN A RATE ERROR***" 350 STOP
/* EXAMPLE IN MICROSOFT C */
#define PORT 0x330 /* base of the 4 ports */
#define RADIX 16 /* for binary counters */
#define FLAG (inp(PORT) & 0x80) /* test for switch flag */
main()
{
long x,y,z,rctr();
int i;
outp(PORT,0); /* clear the counters */
outp(PORT+3,0); /* select status */
if(inp(PORT) & 0x30) /* (bits should be zero) */
{
printf("No board found at port %x\n",PORT);
exit(1);
}
puts("Please press digitizing switch ten times.");
for(i=0; i<10; i++) /* main loop: read & display */
{
inp(PORT+3); /* clear flag */
outp(PORT+3,0); /* select status */
while(!FLAG)
; /* hang waiting for switch */
if(inp(PORT) & 0x40)
{
printf("***THERE HAS BEEN A RATE ERROR***\n");
exit(1);
}
outp(PORT,1); /* copy to holding reg */
inp(PORT+3); /* clear flag */
x = rctr(1);
y = rctr(2);
z = rctr(3);
printf("Data point %2d: x=%8ld, y=%8ld, z=%8ld\n",
i,x,y,z);
}
printf("Ten values read, all done\n");
}
long rctr(c) /* read one counter */
int c;
{
long v;
outp(PORT+3,c); /* select a counter */
v = inp(PORT);
v = v*RADIX + inp(PORT);
v = v*RADIX + inp(PORT);
v = v*RADIX + inp(PORT);
v = v*RADIX + inp(PORT);
v = v*RADIX + inp(PORT);
return(v);
}
Inadequate grounding can produce rate error indications through noisy input signals. The connectors are laid out for flat cable with every third conductor a ground. These grounds should be connected at both ends to keep impedance low and for best shielding. In addition, it is important that the power supply ground go to the encoder independently of the signal ground. If this is not the case, the voltage drop in the shared length of ground will subtract from the TTL noise margin.
Encoder zero detect outputs may be wired to the parallel input port and sensed in software. To establish the reference, the software waits for the zero detect signal, reads the corresponding counter, saves the reading, and subtracts it from all subsequent readings. The accuracy of this method depends both on the width of the zero detect signal and on the input rate. Recall that the counters count on all four state changes of each cycle of the quadrature input. If the zero detect pulse is, for instance, three states wide, the reference when approached from the left will differ by two counts from that when approached from the right. If the inputs change state faster that the software can respond, the reference will differ by the number of intervening counts. This consideration may suggest the use of a machine language subroutine for zero detect.
The input from the operator's switch goes to circuitry that ensures that the FLAG bit is set only once even if the switch bounces multiple times. Both the normally-open and normally-closed contacts must be connected for this circuit to work.
The board encodes each decimal digit as BCD when sending it to the computer (in contrast with the older S-100 model which encoded the digits in ASCII). If the programmer wishes to store the digits as a text string, the ASCII code for '0' (30 hex or 48 decimal) can be added to each digit (in software) as it is input.
This option replaces the eighteen decimal counter chips with eighteen binary counter chips. The maximum count in each of the three registers is extended from 999,999 to 16,777,215. Software should be written with the radix as a parameter.
Interrupts on the bus of the IBM PC are inexplicably high-true. This means
that undriven lines are seen as true and must be masked at the 8259 interrupt
controller. It also precludes 'wired-or' logic, and two devices may share a line
only if they are never both enabled at once.
Therefore, the ENABLE bit in
the SEC-PC 'connects' the FLAG bit, through a driver, and through a jumper, to
the bus. The jumper allows the user to select one of the six interrupt levels
+IRQ2 through +IRQ7. Once asserted on the bus, the interrupt controller at the
processor must be enabled for that level before it will be seen.
The interrupt service routine should be written to copy the counters to the holding register, input the data, clear the FLAG bit, and exit. Applications not using interrupts may safely ignore the ENABLE bit if no interrupt jumper is installed.
|