The effect of pressing the load key on the 1402 is to set a word mark in location 1, clear all word marks in locations 2-80, read a card, and branch to location 1.
Since every instruction has to begin with a word mark, the first card loaded has to start setting word marks for the rest of the program on that card. Fortunately, a seven-character set word mark instruction is one of three instructions that do not need to be terminated by a word mark in the next character.
001 sw 8,12 008 r 1Which on the first card reads
,0080121001Each of the next cards loads one instruction or data field:
001 lca abc,xyz 008 r 1 012 * first character to load ... abc * last character to load at xyzwhich on the card reads
LABCXYZ1001...The last card clears the read area and branches to the program using a seven-character clear storage and branch instruction:
001 cs xyz,80which on the card reads
/xyz080
To bootstrap this loader, Autocoder produces the following card:
....5...10...15...20...25...30...35...40...45...50...55...60...65...70. ,008015,022029,036040,047054,061068,072/061039 ,0010011040 1 1 1 1 1 1 1 1 1 1 1 1A simpler one is
....5...10...15...20...25...30...35...40...45...50...55...60...65...70. ,008047/047046 ,054061,068072,0010401040 1 1 1 1 1 1 1If a program has overlays, it's useful not to clear the word marks in the read area, so as to be able to continue loading. To enter a portion of a program without clearing the read area, columns 68-71 contain a branch instruction.
The last card has a clear storage and branch instruction in columns 40-47.
This is described in detail on page 51 in the Autocoder assembler reference manual.
When the tape load key is pressed, the 1401 reads one record from tape unit 1, with word marks, into location 1, and branches to location 1. It's not necessary to bootstrap this process in the same way as for loading from cards because records can be read from tape with word marks. It may be necessary, however, to provide that one record of the program reads the next one.
Autocoder provides a loader that runs entirely in locations 1-80. The first record clears core:
....5...10...15...20...25...30...35...40...45...50...55...60...65...70. ,200/000H008V0052001L051115L/100099L%U1001R/007199 CLEAR STORAGE 1 1 1 1 1 11 1 1
The second record contains the loader for the remaining records:
....5...10...15...20...25...30...35...40...45...50...55...60...65...70. U%U1B.L%U1020RB001L.020 1 11 1 1 1
which is executed beginning in location 7. Subsequent records load data into core, and then load the next record by branching to location 7.
This is described in detail in on page 51 the Autocoder assembler reference manual.
job Alternative boot loader -- uses SBR
ctl 6611
*
* Boot loader. On each program card
* CC 1-3 give first address to load.
* CC 4-5 give number of non-word-separator characters to process.
* CC 7-70 are characters to be loaded, or word separator
* characters 0-5-8 preceding characters to get word marks.
* Load CS xxx,080 atop read - read&6 to enter program, thus
* 09907~/xxx080
* or change the A-address at done&1 - done&3 to enter the program
* without clearing the read area, thus
* 13103xxx
*
* This runs in 96-199. The start-up code from 200-218 is cleared.
*
sfx 1
org 96
k001 dc 001
read r
sbr move&3,007 Starting from address & 1
loop mcw 3,cwsw&3 Move ,,to,, address to cw or sw
mcw cw Move CW op code to cworsw
mcw 3 Move ,,to,, address to move
s read,5 Decr count of chars to process
ma read-1,003 Bump ,,to,, address
done bm read,5 Read another card if all moved
move mcw 0-0,save Pick up two characters
mcw save-1,0-0 Store character, B gets cc 1-3
cwsw cw 0-0 Either SW or CW, A gets cc 1-3
addrs ma k001,move&3 Bump from address
bce *&5,save-1,~ word separator, 0-5-8
b loop Process next character
s save-1 Clobber word separator
bce addrs,save,~ word separator, 0-5-8
mcw sw,cwsw Prepare to set WM
b move
cw cw
sw sw
save equ 80 Use cc 79-80 for work
first sw 79
cs
sw 1,4
cs read,*
xfr first