Pre-launch Review
RCS FAILURE MONITOR
Scanned pages: 190-192
# Copyright: Public domain.# Filename: RCS_FAILURE_MONITOR.agc# Purpose: Part of the source code for Luminary 1A build 099.# It is part of the source code for the Lunar Module's (LM)# Apollo Guidance Computer (AGC), for Apollo 11.# Assembler: yaYUL# Contact: Hartmuth Gutsche <hgutsche@xplornet.com>.# Website: www.ibiblio.org/apollo.# Pages: 190-192# Mod history: 2009-05-19 HG Transcribed from page images.## This source code has been transcribed or otherwise adapted from# digitized images of a hardcopy from the MIT Museum. The digitization# was performed by Paul Fjeld, and arranged for by Deborah Douglas of# the Museum. Many thanks to both. The images (with suitable reduction# in storage size and consequent reduction in image quality as well) are# available online at www.ibiblio.org/apollo. If for some reason you# find that the images are illegible, contact me at info@sandroid.org# about getting access to the (much) higher-quality images which Paul# actually created.## Notations on the hardcopy document read, in part:## Assemble revision 001 of AGC program LMY99 by NASA 2021112-061# 16:27 JULY 14, 1969
# Page 190# PROGRAM DESCRIPTION## AUTHOR: J S MILLER## MODIFIED 6 MARCH 1968 BY P S WEISSMAN TO SET UP JOB FOR 1/ACCS WHEN THE MASKS ARE CHANGED.## THIS ROUTINE IS ATTACHED TO T4RUPT, AND IS ENTERED EVERY 480 MS. ITS FUNCTION IS TO EXAMINE THE LOW 8 BITS# OF CHANNEL 32 TO SEE IF ANY ISOLATION-VALVE CLOSURE BITS HAVE APPEARED OR DISAPPEARED (THE CREW IS WARNED OF JET# FAILURES BY LAMPS LIT BY THE GRUMMAN FAILURE-DETECTION CIRCUITRY; THEY MAY RESPOND BY OPERATING SWITCHES WHICH# ISOLATE PAIRS OF JETS FROM THE PROPELLANT TANKS AND SET BITS IN CHANNEL 32). IN THE EVENT THAT CHANNEL 32 BITS# DIFFER FROM 'PVALVEST', THE RECORD OF ACTIONS TAKEN BY THIS ROUTINE, THE APPROPRIATE BITS IN 'CH5MASK' &# 'CH6MASK', USED BY THE DAP JET-SELECTION LOGIC, ARE UPDATED, AS IS 'PVALVEST'. TO SPEED UP & SHORTEN THE# ROUTINE, NO MORE THAN ONE CHANGE IS ACCEPTED PER ENTRY. THE HIGHEST-NUMBERED BIT IN CHANNEL 32 WHICH REQUIRES# ACTION IS THE ONE PROCESSED.## THE CODING IN THE FAILURE MONITOR HAS BEEN WRITTEN SO AS TO HAVE ALMOST COMPLETE RESTART PROTECTION. FOR# EXAMPLE, NO ASSUMPTION IS MADE WHEN SETTING A 'CH5MASK' BIT TO 1 THAT THE PREVIOUS STATE IS 0, ALTHOUGH IT OF# COURSE SHOULD BE. ONE CASE WHICH MAY BE SEEN TO EVADE PROTECTION IS THE OCCURRENCE OF A RESTART AFTER UPDATING# ONE OR BOTH DAP MASK-WORDS BUT BEFORE UPDATING 'PVALVEST', COUPLED WITH A CHANGE IN THE VALVE-BIT BACK TO ITS# FORMER STATE. THE CONSEQUENCE OF THIS IS THAT THE NEXT ENTRY WOULD NOT SEE THE CHANGE INCOMPLETELY INCORP-# ORATED BY THE LAST PASS (BECAUSE IT WENT AWAY AT JUST THE RIGHT TIME), BUT THE DAP MASK-WORDS WILL BE INCORRECT.# THIS COMBINATION OF EVENTS SEEMS QUITE REMOTE, BUT NOT IMPOSSIBLE UNLESS THE CREW OPERATES THE SWITCHES AT HALF-# SECOND INTERVALS OR LONGER. IN ANY EVENT, A DISAGREEMENT BETWEEN REALITY AND THE DAP MASKS WILL BE CURED IF# THE MISINTERPRETED SWITCH IS REVERSED AND THEN RESTORED TO ITS CORRECT POSITION (SLOWLY).## CALLING SEQUENCE:## TCF RCSMONIT (IN INTERRUPT MODE, EVERY 480 MS.)## EXIT: TCF RCSMONEX (ALL PATHS EXIT VIA SUCH AN INSTRUCTION)RCSMONEX EQUALS RESUME
# ERASABLE INITIALIZATION REQUIRED:## VIA FRESH START: PVALVEST = +0 (ALL JETS ENABLED)# CH5MASK, CH6MASK = +0 (ALL JETS OK)## OUTPUT: CH5MASK & CH6MASK UPDATED (1'S WHERE JETS NOT TO BE USED, IN CHANNEL 5 & 6 FORMAT)# PVALTEST UPDATED (1.5 WHEN VALVE CLOSURES HAVE BEEN TRANSLATED INTO CH5MASK & CH6MASK; CHAN 32 FORMAT)# JOB TO DO 1/ACCS.## DEBRIS: A, L, Q AND DEBRIS OF NOVAC.## SUBROUTINE CALLED: NOVAC.
EBANK= CH5MASK
BANK 23 SETLOC RCSMONT BANK# Page 191 COUNT* $$/T4RCS
RCSMONIT EQUALS RCSMON
RCSMON CS ZERO EXTEND RXOR CHAN32 # PICK UP + INVERT INVERTED CHANNEL 32. MASK LOW8 # KEEP JET-FAIL BITS ONLY. TS Q
CS PVALVEST # - - MASK Q # FORM PC + PC. TS L # (P = PREVIOUS ISOLATION VALVE STATE, CS Q # C = CURRENT VALVE STATE (CH 32)). MASK PVALVEST ADS L # RESULT NZ INDICATES ACTION REQUIRED.
EXTEND BZF RCSMONEX # QUIT IF NO ACTION REQUIRED.
EXTEND MP BIT7 # MOVE BITS 8 - 1 OF A TO 14 - 7 OF L. XCH L # ZERO TO L IN THE PROCESS.
-3 INCR L DOUBLE # BOUND TO GET OVERFLOW IN THIS LOOP. OVSK # SINCE WE ASSURED INITIAL NZ IN A. TCF -3
INDEX L CA BIT8 -1 # SAVE THE RELEVANT BIT (8 - 1). TS Q MASK PVALVEST # LOOK AT PREVIOUS VALVE STATE BIT. CCS A TCF VOPENED # THE VALVE HAS JUST BEEN OPENED.
CS CH5MASK # THE VALVE HAS JUST BEEN CLOSED. INDEX L MASK 5FAILTAB ADS CH5MASK # SET INHIBIT BIT FOR CHANNEL 5 JET.
CS CH6MASK INDEX L MASK 6FAILTAB ADS CH6MASK # SET INGIBIT BIT FOR CHANNEL 6 JET.
CA Q ADS PVALVEST # RECORD ACTION TAKEN.
TCF 1/ACCFIX # SET UP 1/ACCJOB AND EXIT.
# Page 192VOPENED INDEX L # A VALVE HAS JUST BEEN OPENED. CS 5FAILTAB MASK CH5MASK TS CH5MASK # REMOVE INHIBIT BIT FOR CHANNEL 5 JET.
INDEX L CS 6FAILTAB MASK CH6MASK TS CH6MASK # REMOVE INHIBIT BIT FOR CHANNEL 6 JET.
CS Q MASK PVALVEST TS PVALVEST # RECORD ACTION TAKEN.
1/ACCFIX CAF PRIO27 # SET UP 1/ACCS SO THAT THE SWITCH CURVES TC NOVAC # FOR TJETLAW CAN BE MODIFIED IF CH5MASK EBANK= AOSQ # HAS BEEN ALTERED. 2CADR 1/ACCJOB
TCF RCSMONEX # EXIT.
5FAILTAB EQUALS -1 # CH 5 JET BIT CORRESPONDING TO CH 32 BIT: OCT 00040 # 8 OCT 00020 # 7 OCT 00100 # 6 OCT 00200 # 5 OCT 00010 # 4 OCT 00001 # 3 OCT 00004 # 2 OCT 00002 # 1
6FAILTAB EQUALS -1 # CH 6 JET BIT CORRESPONDING TO CH 32 BIT: OCT 00010 # 8 OCT 00020 # 7 OCT 00004 # 6 OCT 00200 # 5 OCT 00001 # 4 OCT 00002 # 3 OCT 00040 # 2 OCT 00100 # 1