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3.1.1 Bootstrap Loaders
When the CPU is configured as a 2114, 2115, 2116, or 2100, the Basic Binary Loader is initially installed in the
highest 64 words of core memory. The BBL reads an absolute binary program from the paper tape reader into
memory. To execute the loader, the following sequence of commands is used:
ATTACH PTR <tape-image-filename>
SET CPU LOADERENABLE
DEPOSIT S <value>
DEPOSIT P <address>
RESET
GO
...where address is the appropriate loader starting address — 07700 for 4K, 17700 for 8K, 27700 for 12K, 37700 for
16K, 57700 for 24K, or 77700 for 32K. The S-register value is set to 000000 to load the paper tape, 000001 to
verify the paper tape, or 100000 to compare the paper tape to memory. Loader execution ends with one of the
following halt instructions:
• HLT 00 — the tape does not compare with memory; A = value that did not compare.
• HLT 11 — a checksum error occurred; A = expected value, B = calculated value.
• HLT 55 — the load address would overlay the BBL.
• HLT 77 — the end of tape was reached with a successful read.
The loader is automatically disabled when the CPU executes the halt instruction within the loader.
1000-series CPUs contain up to four Initial Binary Loaders stored in ROM. In hardware, a loader is selected by
setting S register bits 15-14 to the ROM number, bits 13-12 and 5-0 to the ROM-specific options, and bits 11-6 to
the device select code. Then the IBL, PRESET, and RUN front-panel buttons are pressed to copy the selected
ROM into the highest 64 words of memory, initialize the I/O device interfaces, and begin execution.
In simulation, the BOOT CPU command implements the IBL-PRESET-RUN facility. The following ROMs are
installed in the CPU:
ROM
Number
Product
Number
Boot Device Description Boot Device
00 12992K 2748B paper tape reader PTR
01 12992A 7900 or 2883 disc DPC or DQC
10 12992D 7970B or 7970E magnetic tape MSC
11 12992B 7905, 7906, 7920, or 7925 disc DS
To execute the loader, the following sequence of commands is used:
ATTACH <dev> <image-filename>
DEPOSIT S <value>
BOOT CPU
The S-register configurations required, supported image file types, and the associated loader halt codes are listed
under their respective devices below. The BOOT CPU command will not report an error if the select code does not
reference the correct device.
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