Source Code
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These source-code files are part of a reconstructed copy of LM131 revision 1,
the final release of the Apollo 13 Lunar Module (LM) Apollo Guidance Computer
(AGC) software.
The source reconstruction began with source code of Luminary 131 previously
transcribed from a digitized copy of that program. A dump of the flight spare
core rope memory module B5, part number 2010802-171, serial number RAY 411,
was obtained. This module is the only module different between Luminary 131
and LM131 revision 1. The dump was disassembled and all changes were incorporated
into these source files. Note that page numbers in the reconstructed code match
those on the Luminary 131 printout, although the changed code would likely have
changed page numbers for a real LM131 revision 1 listing.
Comments from the original source code are prefixed with a single '#' symbol,
whereas comments added later are prefixed by "##" or "###". Report any errors
noted by creating an
issue report at the Virtual AGC
project's GitHub repository.
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033316,000002: ## Copyright: Public domain.
033317,000003: ## Filename: THROTTLE_CONTROL_ROUTINES.agc
033318,000004: ## Purpose: A section of LM131 revision 1.
033319,000005: ## It is part of the reconstructed source code for the final
033320,000006: ## release of the flight software for the Lunar Module's (LM)
033321,000007: ## Apollo Guidance Computer (AGC) for Apollo 13. The code has
033322,000008: ## been reconstructed from a listing of Luminary 131 and a dump
033323,000009: ## of a core rope memory module B5, part number 2010802-171,
033324,000010: ## which is the only module different between LM131 revision 1
033325,000011: ## and Luminary 131. The executable generated from this source
033326,000012: ## has been verified against the module dump, so while the names,
033327,000013: ## comments, and ordering may not be exactly correct, the
033328,000014: ## resulting binary is.
033329,000015: ## Reference: pp. 788-792
033330,000016: ## Assembler: yaYUL
033331,000017: ## Contact: Ron Burkey <info@sandroid.org>.
033332,000018: ## Website: www.ibiblio.org/apollo/index.html
033333,000019: ## Mod history: 2022-10-28 MAS Created from Luminary 131.
033334,000020:
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Page 788
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033336,000022: 31,2144 BANK 31
033337,000023: 31,2000 SETLOC FTHROT
033338,000024: 31,2000 BANK
033339,000025: 31,2144 E7,1612 EBANK= PIF
033340,000026: 31,2144 COUNT* $$/THROT
033341,000027:
033342,000028: # * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
033343,000029: # HERE FC, DESIRED THRUST, AND FP, PRESENT THRUST, UNWEIGHTED, ARE COMPUTED.
033344,000030:
033345,000031: 31,2144 31245 THROTTLE CA ABDELV # COMPUTE PRESENT ACCELERATION IN UNITS OF
033346,000032: 31,2145 00006 EXTEND # 2(-4) M/CS/CS, SAVING SERVICER TROUBLE
033347,000033: 31,2146 72356 MP /AF/CNST
033348,000034: 31,2147 00006 +3 EXTEND
033349,000035: 31,2150 23607 QXCH RTNHOLD
033350,000036: 31,2151 02337 AFDUMP TC MASSMULT
033351,000037: 31,2152 53470 DXCH FP # FP = PRESENT THRUST
033352,000038: 31,2153 00006 EXTEND
033353,000039: 31,2154 31464 DCA /AFC/
033354,000040: 31,2155 02337 TC MASSMULT
033355,000041: 31,2156 55615 TS FC # FC = THRUST DESIRED BY GUIDANCE
033356,000042: 31,2157 53466 DXCH FCODD # FCODD = WHAT IT IS GOING TO GET
033357,000043:
033358,000044: # COMPUTE DESIRED THRUST FOR DISPLAY AS A PERCENTAGE OF 10,500 POUNDS
033359,000045:
033360,000046: 31,2160 32360 CAF 4FMAXNOM # MOVE 4FMAXNOM TO ERASABLE FOR DV BELOW
033361,000047: 31,2161 54002 TS Q
033362,000048: 31,2162 31615 CA FC
033363,000049: 31,2163 72357 MASK OCT17777 # FOR SAFETY
033364,000050: 31,2164 00006 EXTEND
033365,000051: 31,2165 10002 DV Q
033366,000052: 31,2166 00006 EXTEND
033367,000053: 31,2167 75003 MP 4SECS
033368,000054: 31,2170 55750 TS THRDISP # FOR DISPLAY IN N92
033369,000055:
033370,000056: # IF IT HAS BEEN LESS THAN 3 SECONDS SINCE THE LAST THROTTLING, AUGMENT FP USING THE FWEIGHT CALCULATED THEN.
033371,000057:
033372,000058: 31,2171 41617 CS TTHROT # THIS CODING ASSUMES A FLATOUT WITHIN
033373,000059: 31,2172 60025 AD TIME1 # 80 SECONDS BEFORE FIRST THROTTLE CALL
033374,000060: 31,2173 74733 MASK POSMAX
033375,000061: 31,2174 40000 COM
033376,000062: 31,2175 65002 AD 3SECS
033377,000063: 31,2176 00006 EXTEND
033378,000064: 31,2177 62203 BZMF WHERETO # BRANCH IF (TIME1-TTHROT +1) > 3 SECONDS
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Page 789
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033380,000066: 31,2200 00006 EXTEND
033381,000067: 31,2201 31611 DCA FWEIGHT
033382,000068: 31,2202 21470 DAS FP
033383,000069:
033384,000070: # THIS LOGIC DETERMINES THE THROTTLING IN THE REGION 10% - 94%. THE MANUAL THROTTLE, NOMINALLY SET AT
033385,000071: # MINIMUM BY ASTRONAUT OR MISSION CONTROL PROGRAMS, PROVIDES THE LOWER BOUND. A STOP IN THE THROTTLE HARDWARE
033386,000072: # PROVIDES THE UPPER.
033387,000073:
033388,000074: 31,2203 35014 WHERETO CA EBANK5 # INITIALIZE L*WCR*T AND H*GHCR*T FROM
033389,000075: 31,2204 54003 TS EBANK # PAD LOADED ERASABLES IN W-MATRIX
033390,000076: 31,2205 E5,1506 EBANK= LOWCRIT
033391,000077: 31,2205 00006 EXTEND
033392,000078: 31,2206 31507 DCA LOWCRIT
033393,000079: 31,2207 52131 DXCH L*WCR*T
033394,000080: 31,2210 35016 CA EBANK7
033395,000081: 31,2211 54003 TS EBANK
033396,000082: 31,2212 E7,1612 EBANK= PIF
033397,000083: 31,2212 44755 CS ZERO # INITIALIZE PIFPSET
033398,000084: 31,2213 55606 TS PIFPSET
033399,000085: 31,2214 40131 CS H*GHCR*T
033400,000086: 31,2215 61620 AD FCOLD
033401,000087: 31,2216 00006 EXTEND
033402,000088: 31,2217 62231 BZMF LOWFCOLD # BRANCH IF FCOLD < OR = HIGHCRIT
033403,000089: 31,2220 40130 CS L*WCR*T
033404,000090: 31,2221 61465 AD FCODD
033405,000091: 31,2222 00006 EXTEND
033406,000092: 31,2223 62226 BZMF FCOMPSET # BRANCH IF FC < OR = LOWCRIT
033407,000093: 31,2224 31467 CA FP # SEE NOTE 1
033408,000094: 31,2225 12236 TCF FLATOUT1
033409,000095:
033410,000096: 31,2226 42002 FCOMPSET CS FMAXODD # SEE NOTE 2
033411,000097: 31,2227 61467 AD FP
033412,000098: 31,2230 12240 TCF FLATOUT2
033413,000099:
033414,000100: 31,2231 40131 LOWFCOLD CS H*GHCR*T
033415,000101: 31,2232 61465 AD FCODD
033416,000102: 31,2233 00006 EXTEND
033417,000103: 31,2234 62241 BZMF DOPIF # BRANCH IF FC < OR = HIGHCRIT
033418,000104:
033419,000105: 31,2235 32003 CA FMAXPOS # NO: THROTTLE-UP
033420,000106: 31,2236 53466 FLATOUT1 DXCH FCODD
033421,000107: 31,2237 34737 CA FEXTRA
033422,000108: 31,2240 55606 FLATOUT2 TS PIFPSET
033423,000109:
033424,000110: # NOTE 1 FC IS SET EQUAL TO FP SO PIF WILL BE ZERO. THIS IS DESIRABLE
033425,000111: # AS THERE IS ACTUALLY NO THROTTLE CHANGE.
033426,000112:
033427,000113: # NOTE2 HERE, SINCE WE ARE ABOUT TO RETURN TO THE THROTTLEABLE REGION
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Page 790
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033429,000115: # (BELOW 55%) THE QUANTITY -(FMAXODD-FP) IS COMPUTED AND PUT
033430,000116: # INTO PIFPSET TO COMPENSATE FOR THE DIFFERENCE BETWEEN THE
033431,000117: # NUMBER OF BITS CORRESPONDING TO FULL THROTTLE (FMAXODD) AND THE
033432,000118: # NUMBER CORRESPONDING TO ACTUAL THRUST (FP). THUS THE TOTAL
033433,000119: # THROTTLE COMMAND PIF = FC - FP - (FMAXODD - FP) = FC - FMAXODD.
033434,000120:
033435,000121: 31,2241 03677 DOPIF TC FASTCHNG
033436,000122: 31,2242 00006 EXTEND
033437,000123: 31,2243 31466 DCA FCODD
033438,000124: 31,2244 55620 TS FCOLD
033439,000125: 31,2245 53613 DXCH PIF
033440,000126: 31,2246 00006 EXTEND
033441,000127: 31,2247 41470 DCS FP
033442,000128: 31,2250 21613 DAS PIF # PIF = FC - FP, NEVER EQUALS +0
033443,000129:
033444,000130: 31,2251 31612 DOIT CA PIF
033445,000131: 31,2252 61606 AD PIFPSET # ADD IN PIFPSET, WITHOUT CHANGING PIF
033446,000132: 31,2253 55614 TS PSEUDO55
033447,000133: 31,2254 54055 TS THRUST
033448,000134: 31,2255 34750 CAF BIT4
033449,000135: 31,2256 00006 EXTEND
033450,000136: 31,2257 05014 WOR CHAN14
033451,000137: 31,2260 30025 CA TIME1
033452,000138: 31,2261 55617 TS TTHROT
033453,000139:
033454,000140: # SINCE /AF/ IS NOT AN INSTANTANEOUS ACCELERATION, BUT RATHER AN "AVERAGE" OF THE ACCELERATION LEVELS DURING
033455,000141: # THE PRECEEDING PIPA INTERVAL, AND SINCE FP IS COMPUTED DIRECTLY FROM /AF/, FP IN ORDER TO CORRESPOND TO THE
033456,000142: # ACTUAL THRUST LEVEL AT THE END OF THE INTERVAL MUST BE WEIGHTED BY
033457,000143: # PIF(PPROCESS + TL) PIF /PIF/
033458,000144: # FWEIGHT = ------------------ + -------------
033459,000145: # PGUID 2 PGUID FRATE
033460,000146: # WHERE PPROCESS IS THE TIME BETWEEN PIPA READING AND THE START OF THROTTLING, PGUID IS THE GUIDANCE PERIOD, AND
033461,000147: # FRATE IS THE THROTTLING RATE (32 UNITS PER CENTISECOND). PGUID IS EITHER 1 OR 2 SECONDS. THE "TL" IN THE
033462,000148: # FIRST TERM REPRESENTS THE ENGINE'S RESPONSE LAG. HERE FWEIGHT IS COMPUTED FOR USE NEXT PASS.
033463,000149:
033464,000150: 31,2262 31762 CA THISTPIP +1 # INITIALIZE FWEIGHT COMP AS IF FOR P66
033465,000151: 31,2263 54130 TS BUF
033466,000152:
033467,000153: 31,2264 41010 CS MODREG # ARE WE IN FACT IN P66?
033468,000154: 31,2265 62452 AD DEC66
033469,000155: 31,2266 00006 EXTEND
033470,000156: 31,2267 12274 BZF FWCOMP # YES
033471,000157:
033472,000158: 31,2270 31234 CA PIPTIME +1 # NO: INITIALIZE FOR TWO SECOND PERIOD
033473,000159: 31,2271 54130 TS BUF
033474,000160: 31,2272 35003 CAF 4SECS
033475,000161: 31,2273 12275 TCF FWCOMP +1
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Page 791
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033477,000163:
033478,000164: 31,2274 35000 FWCOMP CAF 2SECS
033479,000165: 31,2275 54002 +1 TS Q
033480,000166: 31,2276 00006 EXTEND
033481,000167: 31,2277 74746 MP BIT6
033482,000168: 31,2300 22131 LXCH BUF +1
033483,000169: 31,2301 40130 CS BUF # TIME OF LAST PIPA READING.
033484,000170: 31,2302 60025 AD TIME1
033485,000171: 31,2303 62004 AD THROTLAG # COMPENSATE FOR ENGINE RESPONSE LAG
033486,000172: 31,2304 74357 MASK LOW8 # MAKE SURE SMALL AND POSITIVE
033487,000173: 31,2305 22007 ZL
033488,000174: 31,2306 00006 EXTEND
033489,000175: 31,2307 10002 DV Q
033490,000176: 31,2310 00006 EXTEND
033491,000177: 31,2311 71612 MP PIF
033492,000178: 31,2312 60000 DOUBLE
033493,000179: 31,2313 53611 DXCH FWEIGHT
033494,000180: 31,2314 11612 CCS PIF
033495,000181: 31,2315 64753 AD ONE
033496,000182: 31,2316 12320 TCF +2
033497,000183: 31,2317 64753 AD ONE
033498,000184: 31,2320 00006 EXTEND
033499,000185: 31,2321 71612 MP PIF
033500,000186: 31,2322 00006 EXTEND
033501,000187: 31,2323 10131 DV BUF +1
033502,000188: 31,2324 22007 ZL
033503,000189: 31,2325 21611 DAS FWEIGHT
033504,000190:
033505,000191: 31,2326 01607 THDUMP TC RTNHOLD
033506,000192:
033507,000193: # FLATOUT THROTTLES UP THE DESCENT ENGINE, AND IS CALLED AS A BASIC SUBROUTINE.
033508,000194:
033509,000195: 31,2327 34737 FLATOUT CAF BIT13 # 4096 PULSES
033510,000196: 31,2330 55606 WHATOUT TS PIFPSET # USE PIFPSET SO FWEIGHT WILL BE ZERO
033511,000197: 31,2331 44755 CS ZERO
033512,000198: 31,2332 55620 TS FCOLD
033513,000199: 31,2333 55612 TS PIF
033514,000200: 31,2334 00006 EXTEND
033515,000201: 31,2335 23607 QXCH RTNHOLD
033516,000202: 31,2336 12251 TCF DOIT
033517,000203:
033518,000204: # MASSMULT SCALES ACCELERATION, ARRIVING IN A AND L IN UNITS OF 2(-4) M/CS/CS, TO FORCE IN PULSE UNITS.
033519,000205:
033520,000206: 31,2337 00006 MASSMULT EXTEND
033521,000207: 31,2340 22130 QXCH BUF
033522,000208: 31,2341 52155 DXCH MPAC
033523,000209: 31,2342 07106 TC DMP
033524,000210: 31,2343 01243 ADRES MASS
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Page 792
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033526,000212: 31,2344 07106 TC DMP # LEAVES PROPERLY SCALED FORCE IM MPAC
033527,000213: 31,2345 02005 ADRES SCALEFAC
033528,000214: 31,2346 07262 TC TPAGREE
033529,000215: 31,2347 30154 CA MPAC
033530,000216: 31,2350 00006 EXTEND
033531,000217: 31,2351 12354 BZF +3
033532,000218: 31,2352 34733 CAF POSMAX
033533,000219: 31,2353 00130 TC BUF
033534,000220: 31,2354 52156 DXCH MPAC +1
033535,000221: 31,2355 00130 TC BUF
033536,000222:
033537,000223: # CONSTANTS:-
033538,000224:
033539,000225: 31,2356 4737 FEXTRA = BIT13 # FEXT +5.13309020 E+4
033540,000226:
033541,000227: 31,2356 04143 /AF/CNST DEC .13107
033542,000228:
033543,000229: 31,2357 17777 OCT17777 OCT 17777
033544,000230: 31,2360 35074 4FMAXNOM DEC 14908 B-14 # EQUIVALENT TO 10,500 LBS.
033545,000231:
033546,000232: # * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
End of include-file THROTTLE_CONTROL_ROUTINES.agc. Parent file is MAIN.agc