The current widespread use of microcomputers has led to the creation of some very low-cost instrumentation. A Pulse Code Modulation (PCM) storage device/data analyzer -- a peripheral plug-in board especially constructed to enable a personal computer to store and analyze data from a PCM source -- was designed and built for use on the NASA Sounding Rocket Program for PMC encoder configuration and testing. This board and custom-written software turns a computer into a snapshot PCM decommutator which will accept and store many hundreds or thousands of PCM telemetry data frames, then sift through them repeatedly. These data can be converted to any number base and displayed, examined for any bit dropouts or changes (in particular, words or frames), graphically plotted, or statistically analyzed

Massey, D. E.

English

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I 
NASA 
Tech n I ca i 
Paper 
2629 
1986 
c 
National Aeronautics 
and Space Administration 
Scientific and Technical 
Information Branch I 
Pulse Code Modulation (PCM) 
Data Storage and Analysis 
Using a Microcomputer 
David E. Massey 
Goddard Space Flight Center 
Wallops Flight Facility 
Wallops Island, Virginia 
PULSE CODE MODULATION (PCM) DATA 
SrORAGE AND ANALYSIS USING A MI- 
David E. Massey 
NASA W d a r d  Space Fl ight  Center 
Wallops Flight Fac i l i t y  
Wallops Island, VA 23337 
Within t h e  last few years, as Sounding 
Rocket Program ac t iv i ty  increased, more 
and more FCM encoders had to  be config- 
ured and programned t o  transmit data fran 
these rocket payloads. The configuration 
and format are unique to  t h e  vehicle  and 
are rare ly  t h e  same. 
configured by programning an EPROM memory 
with t h e  appropriate word and frame 
s t ruc ture  to  accormrxlate a l l  t h e  science 
and housekeeping data channels. 
The encoder is 
Figure 1 
m D r C W l I I I u I  
Figure 1.-Sounding rocket FCM data  l i nk  
shows a typical way da ta  is transnitted 
t o  the  ground using FCM. 
expected, when output increases,  so do 
t h e  problem due t o  the  everchanging PCM 
encoder configurations and f o m t  pro- 
graming. 
Wallops Fl ight  Fac i l i t y  t o  examine these 
PCM encoders has been t o  u t i l i z e  a stan- 
dard PCM d e c m t a t o r ,  word selector, and 
s t r i p  char t ,  which do t h e  job but are 
time-consuming. Clearly,  a better, 
f a s t e r ,  mre in t e l l i gen t  method of 
examining t h e  encoders was needed. This 
device would be capable of d e c m t a t i n g  
and s to r ing  PCM telemetry da ta  frames for 
display and analysis ,  helping t o  speed up 
configuration. 
As would be 
The method used f o r  years at 
The current widespread use of micro- 
computers has led  t o  t h e  creation of 
very low-cost instrumentation. A PCM 
storage device/data analyzer was designed 
and b u i l t  for use on the  NASA Sounding 
Rocket Program f o r  PCM encoder configura- 
t i on  and tes t ing .  This storage device/ 
data analyzer is a per ipheral  plug-in 
board especial ly  constructed to  enable a 
personal cuqmter  to  store and analyze 
data f r o m  a PCM source. 
custan-written software tu rn  t h e  
computer i n t o  a snapshot FCM decarmutator 
which w i l l  accept and store many hundreds 
or thousands of PCM telemetry data frames, 
then s i f t  through them repeatedly. 
data can be converted to  any number base 
and displayed; examined for any b i t  drop- 
outs  or changes -- i n  pa r t i cu la r ,  mrds 
or frames; graphically p lo t ted ;  or sta- 
t i s t i c a l l y  analyzed. These methods help 
t o  solve encoder problem. 
This board and 
These 
DIGITAL INPUTS 
Dl - DIGITAL 
02 - wx 
PFiOBLEM SOLVING 
%% PCMWTPUT 
WX 
Channel Cross Talk.4ne of t h e  most 
evasive problem encountered i n  PCM 
encoders is channel cross t a l k .  For 
example, when stimulating a pa r t i cu la r  
channel or channels on an encoder (see 
Figure 2) ,  an adjacent channel w i l l  pro- 
ANALOG INWTS 
Figure 2.-pcM encoder 
duce a b i t  or tm i n t e m i t t e n t l y  or 
ac tua l ly  f o l l o w  a s igna l  t h a t  it was not 
programed to  pick up. 
shown t h a t  t h e  storage device w i l l  m r k  
w e l l  i n  t h i s  problem area, i f  you take 
t h e  cross t a l k  channel as a s top  t r i g g e r ,  
which enables t h e  storage device to  
f reeze  t h e  thousand or so frames previous 
t o  t h e  occurrence of t h e  cross t a l k .  
This allows examination of o ther  channels 
p r i o r  to  t h e  event i n  question. 
Experience has  
Renegade Encoder.-This is an encoder which 
is output t ing PCM data but w i l l  not hold 
solid frame sync lock on a decmmutator. 
The storage device w i l l  take i n  these  
frames and display them, t h e  operator can 
sift through t h i s  data t o  locate t h e  
p a r t i a l  frame sync pa t te rn ,  or determine 
t h a t  there is no pa t te rn  which i n  tu rn  
should lead t o  correct ing t h e  problem. 
Cumutation.-Super- or sub-carmutated 
words can e a s i l y  be evaluated f o r  correct 
posi t ioning within t h e  frame. B i t  
g l i t ches  and unknown changes can be seen 
using the  graph p lo t  mode by s t h l a t i n g  
t h e  channel i n  question with a known sig- 
na l ;  t h i s  can be displayed on a graph. 
If any b i t  anomalies occur, they w i l l  be 
seen on t h i s  p ic ture .  
frequency s igna l  with tm-bit  g l i t ches  
is shown i n  Figure 3. 
A typ ica l  low- 
The PCM storage device can, of course, be 
2 
I 
TABLF: I .-KN FRAME DISPLAY 
PCM FRRME # 1 
WORD DRTR DECIMQL 
Figure 3.-Graph mode p lo t  of word 
showing b i t  g l i t c h e s  
MTA MTA MTA MTA MTA DATA DATA 
POI MTA F R m  
FS * FWME SVIKHROIIIZATIOI( PATTERll 
0 1 0 1 1 1 1  O l O l l  
W 
Figure 4.-FCM frame 
used to  ve r i fy  correct number of words i n  
a frame, correct word posi t ion (see 
Figure 41, and correct data i n  a par t ic -  
u l a r  subframe. By examining s tored  
frames i n  a w r d  comparison mode, incor- 
rect data can be found. A typ ica l  frame 
displayed on screen  with decimal value 
conversions is shown i n  Table I .  
FS 
2 
3 
4 
5 
6 
7 
8 
3 
18 
NFS 
841118184188 
8118881811 
818841841118 
881411181418 
88818141888 
8181888881 
814184188181 
88418818188 
8881818888 
8181888881 
81418888888 
HARDWARE 
288 
395 
188 
88 
321 
26 1 
28 
88 
32 1 
256 
s62 
The hardware of t h i s  device is remarkably 
simple, consis t ing mainly of a plug-in 
per ipheral  board (see Figure 5). The 
board contains  16 ki lobytes  of static 
RAM, address counter/demder,  byte 
counter, control  logic, s h i f t  r e g i s t e r ,  
and PIA i n t e r f ace  port. The 16-kilobyte 
RAM has 131,072 bi t s  i n  it, which is t h e  
present capacity of FCM storage. The FCM 
U m R  
L I 
Figure 5.-Hasdware block diagram of 
plug-in board 
3 
data en te r s  t h e  s h i f t  register t o  be 
converted t o  8-bit-wide data. 
nothing t o  do with t h e  size of t h e  FCM 
word i n  t h e  format.) After it is convert- 
TABLE II.-SXTWAFU3 0 MENU 
COMMFIND MENU 
(This has  
SPFICE ERR * GO TO NEXT FRFIME OF DQTR 
P = PREVIOUS SCREEN OF DRTR 
ed, then it is stored i n  RAM. Once W = SELECT WORDS 
started i n t o  operation, t h i s  is a window- N = NEXT FRRME 
E = EFICK UP TO PREVIOUS FRFIME 
F = SELECT R FRRME 
ing device; i.e., t h e  latest PCM data is 
always being stored i n  RAM. When t h e  
device is given a s top  t r igge r ,  e i t h e r  G = GRFIPH DRTF) 
L = LORD NEW DRTR I N T O  MEMORY 
Q = Q U I T  
m u a l l y  or automitically,  t h e  last 
131,072 b i t s  t h a t  were transmitted are 
PRESS 'M'  FOR I N F O  ON SCROLLING. 
frozen. The present board has  been tested COMMFIND? 
t o  f i v e  mil l ion bits  per second (MBPS) 
with no anomalies. After  storage of data, a pa r t i cu la r  word and scanning a l l  o ther  
t h e  microccmputer starts to  load b i t s  frames f o r  t h i s  mrd. This mode can also 
from t h e  storage device RAM i n t o  main select and examine frames of data i n  
computer RAM and begins  t o  process these  sequence and at random. 
b i t s  according t o  t h e  appropriate software mode is a very valuable tool. 
The graph p lo t  
I t  allows 
algorithm. 
mFTwARE 
As with most microcomputer instruments 
(any computer application f o r  t h a t  
matter), software is the  key to a good 
system. In keeping with t h i s  thought, 
tine storage device has sane long, f a i r l y  
complex software writ ten f o r  its opera- 
t ions .  The software operates i n  three  
tmin modes: frame display/scan, graph 
p l o t ,  and m r d  canpare (see Table 11). 
The frame display/scan mode o f f e r s  screen 
display of a frame of data (as i n  Table 
I )  grouped i n t o  words and numbered. This 
data can be examined fur ther  by se lec t ing  
t h e  se lec t ion  of a pa r t i cu la r  word i n  a 
FCM frame and p l o t s  t h i s  word i n  every 
stored frame on a graph. 
e f fec t ive ly  a graphical digital-to-analog 
converter. The last mode is t h e  word 
compare mode; t h i s  allows comparison of a 
mrd or words i n  a l l  stored frames. These 
comparisons can be f o r  changes i n  data 
valiles or o ther  statistical f u c t i o n s .  
This is 
EXPANSION 
Obviously, 131,072 b i t s  of FCM storage 
are not enough when dealing with PCM 
s y s t e m  approaching one MEPS. A new 
board containing two t o  eight mil l ion 
b i t s  is being designed using t h e  new 
4 
252K dynamic RAM chips,  thus raising t h e  
complexity of the  hardware s l i gh t ly .  
only changes i n  software are t o  increase 
1 pointer  addresses to  be able t o  read al l  
I storage RAM. Using the  256K dynamic RAM 
r 
The 
and a LSI cont ro l le r ,  t he  capabi l i ty  of 
eight mi l l ion  b i t s  e x i s t s  on one board. 
This m u l d  represent a n i c e  amxlnt of 
storage,  say 10 seconds of data at 800K 
bits/second or about 50,OOO frames of 
average size. 
1 
I This instrument does not t r y  t o  do it a l l ;  
1 it is no match for a real-time telemetry 
data processing canputer (which costs 
hundreds of thousands of do l l a r s ) .  I t  
does f i l l  a void f o r  which no su i t ab le  
replacement could be found for such a 
low cost. 
I 
, 
I 
I 
I NASA Goddard Space Fl ight  Center 
1 
Wallops Fl ight  Fac i l i t y  
Wallops Island, VA 23337 
August 1985 
5 
I. Report No. 2. Government Accession No. 
NASA TP-2629 
4. Title and Subtitle 
Pulse Code Modulation (Fcw) D a t a  Storage and 
Analysis Using a Microcargxlter 
David E. Massey 
7. Author(s) 
3. Recipient's Catalog No. 
5. Report Date 
A u w t  1986 
822.3 
6. Performing Organization Code 
8. Performing Organization Report No. 
6. Abstract 
The current widespread use of microcanputers has l e d  to  t h e  creat ion of sane very low-cost 
instrumentation. A p(M storage device/data analyzer -- a peripheral  plug-in board especially 
constructed t o  enable a personal ccmputer to  store and analyze data f r a n  a PCM souzce -- was 
designed and built f o r  use on t h e  NASA Sounding Rocket Program f o r  Fcw encoder configuration 
and tes t ing .  This board and custan-mitten software turns  a ccmputer i n t o  a snapshot FCM 
decarmutator which w i l l  accept and store many hundreds or thousands of Fcw telemetry data 
frames, then s i f t  through than repeatedly. 
and displayed, examined f o r  any b i t  dropouts or changes ( i n  par t icu lar ,  words or frames), 
graphically plotted,  or s t a t i s t i c a l l y  analyzed. 
These data can be converted to  any number base 
~ 
9. Performing Organization Name and Address 
NASA Goddard Space Fl ight  Center 
Wallops Fl ight  Faci l i ty  
Wallops Island, VA 23337 
2. Sponsoring Agency Name and Address 
National Aeronautics and Space Achinistration 
Washington, DC 20546 
17. Key Words (Suggested by Author(s)) 18. Distribution Statement 
10. Work Unit No. 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
NASA Technical Paper 
14. Sponsoring Agency Code 
Decarmutators 
Telanetry D a t a  Canpression 
21. No. of Pages 19. Security Classif. (of this report) 20. Security Classif. (of this page) 
Unclassified Unclassified 8 
Unclassified - unlimited 
STAR Category 32 
22. Price' 
A02 
For sale by the National Technical Information Service, Springfield, Virginia 22161 NASA-Langley, 1986 


Pulse Code Modulation (PCM) data storage and analysis using a microcomputer

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