One of the software products Hewlett-Packard produced for the early 211x series machines was a single-user BASIC interpreter. Around 2010 a version of the assembly source, dating from 1970, for the interpreter and associated configuration program became available on bitsavers. This was thanks to Guy Sotomayor who had kept it around since high school in 1971.

This article descibes the requirements and process to get the HPBASIC interpreter to run on a 211x-series processor, starting if necessary from the original HP assembler source.

Historical Note

BASIC was originally (1964) developed on and targetted for multi-user time-shared systems. The early home computer market of the late-1970s to 1980s would largely be characterised by boot-to-BASIC machines: small machines with a BASIC interpreter in ROM which at power-on would immediately boot that interpreter and present BASIC ready to use, machines such as the Apple II, Commodore PET, TRS-80, etc.

Between the large time-shared systems and the small boot-to-BASIC machine, a few waypoint developments can be identified. The earliest (known to this author) instance of a ROM-based BASIC machine is the HP-9830 (1972), followed by the Wang 2200 (1973) and IBM 5100 (1975). Single-user HP BASIC is an even earlier waypoint.

The available assembler source for Single-user HP BASIC is dated January 1970. An HP computer products brochure from June 1968 lists an "interpretative compiler" for BASIC, "operable in 8K" - this being distinct from the HP2000 Timeshared BASIC system for the 2116, also available by 1968.

Single-user HP BASIC could be used as a stand-alone system - it did not require the presence of an OS or executive, nor did it have to sequentially overlay or reload segments of the system to accomplish functionality. Once an HP BASIC system was in core, it was a stand-alone system requiring only the computer and teletype/console for entry and execution of BASIC programs. Combining this stand-alone ability with the non-volatility of core memory, it is possible to have the BASIC "READY" prompt in 2 seconds (3 button-pushes) from power-on of the computer. An HP-2116 with HP BASIC in 1968 may have been the first "boot-to-BASIC" system, though not quite boot-to-BASIC-at-power-on.

Contents (this page): System Requirements Running HPBASIC Supported Language & Commands Using HPBASIC Some Simple Programs

Sub-pages: Memory Map Operation Examples

Resources: HPBASIC Listing and ABS Files (.tgz) HPBASIC User Manual (.pdf) (extract from "A Pocket Guide to Hewlett-Packard Computers", 7/70) Basic Binary Loaders

External: Source for HPBASIC at bitsavers 211x Students Manual 1968/9, BASIC - Section XII, pdf.336

System Requirements

Processor

8KW minimum of memory is required. For an 8KW system using the bufferred I/O option, there will be ~ 2.1KW available for the user program and runtime needs.

Console

In a modern context a console teletype may be simulated with an async serial-line communication program running on some host machine. Such a setup will be referred to here as the console-host. The interpreter usually outputs the 8th bit set 1, so the receiving console-host needs the ability to ignore it. SCOMM is a recommendation for such a program, providing for both text-based console operation and text or binary-transparent transfer of files.

Storage

In the modern context, loading and saving files via a console-host as simulated paper-tape reader and punch is the simple solution.

Running HP BASIC

As software, an HPBASIC System is comprised of two program elements:

• the HPBASIC interpreter,
• an I/O driver package configured for use with the target hardware.

An I/O Package is produced by running the configuration program PBS (Prepare BASIC System) on the period HP machine. PBS contains template device drivers and produces an I/O Package based on input responses when it is run.

The full workflow starting from assembler source to a running HPBASIC System is shown in the following diagram:

This process can be entered from several starting points depending on the initial availability of the internally-generated resources.

• Stage 1: Starting from assembler source.
  The HPBASIC interpreter is contained in 11 assembly source files, the PBS configuration program is in another 3 assembly source files. Assembly produces .abs files which contain loadable machine code.

• Stage 2: Starting from assembled HPBASIC and PBS load files (pbs.abs & hpbasic.abs).
  The objective here is to produce an I/O Package configured to the target hardware setup. Operation of PBS is discussed in a following section.
  See PBS Execution Example.

• Stage 3: Starting from an assembled HPBASIC System file(s).
  With the two HPBASIC System program elements available, in either one or two files, these files can be loaded via the BBL. An I/O Package configured for 8KW memory, and a 12531B/C/D serial I/O interface at channel 11 is available as an assembled & loadable machine-code file (hpbsys.abs).
  See System Load & Run Example.

• Stage 4: Starting from HPBASIC System already in core.
  Once the HPBASIC System has been loaded into core, it can be restarted even after a power-down cycle thanks to the non-volatility of core. At power-up, assuming the data switches are left at the HPBASIC start address of 0100, booting is just 3 button-pushes on a 2116: PRESET, LOAD-ADDRESS, RUN.
  See Restarting Example.

If HPBASIC is loaded at step 2.2b, before PBS is run, PBS will produce an absolute tape with both the configured I/O package and the HPBASIC interpreter, thus a single boot tape. Otherwise, the output from PBS will contain only the configured I/O package and loading the complete HPBASIC System is two steps: loading the I/O package (step 3.1a) and loading the interpreter (step 3.1b). In either case, HPBASIC must be loaded after it's compatriot as it intentionally overwrites some memory locations.

Also, if HPBASIC was loaded, after running PBS it is permissible to skip step 7 and run the now-configured BASIC system directly from core. Note though, that to do so one must not allow PBS to dump (punch) the configured system. Apparently PBS corrupts the in-core system in the course of dumping it, attempting to run the in-core system after dumping will result in BASIC responding with "ERROR IN LINE " to all input.

The Memory Map presents more details about the program elements and their organisation in core.

PBS Execution

PBS obtains configuration information from both the front panel Sense switches and from queries via the console.

PBS provides a configuration option for "buffered" or "serial" TTY driver. This does not refer to a line or multi-character buffer in memory, or a serial versus parallel interface. It refers to which of the HP serial I/O interfaces is present in the processor for communication with the TTY/console:

• The 12531A is a bit-banged async serial interface, it is essentially a 1-bit I/O interface, the serialisation has to be done in software. This would be the "serial" option.
• The 12531B,C,D async serial interfaces have a one-character hardware buffer (register) and do the serialisation in hardware, more akin to a modern UART. This would be the "buffered" option.

When run, PBS performs the following sequence of activities:

1. Select the bufferred or serial I/O driver for the TTY/console, based on Sense-switch 15.
   If switch 15 is down, buffered is selected:
   • When PBS was loaded, the I/O driver links were initially set to point to the routines in the bufferred I/O driver, and LWAM is appropriate for this driver.
   If switch 15 is up, serial is selected:
   • The serial driver is moved to overwrite the bufferred driver.
   • Set the driver links to the serial driver.
   • Set LWAM appropriately.
   The device channel address is now set in the selected driver, as indicated by Sense-switches 0-5. The now-configured TTY/console driver is used for both the following PBS queries and for incorporation in the I/O Package for use by the interpreter.
2. Query: PHOTO READER I/O ADDRESS?
   This is the device used by the interpreter PTAPE command for loading user programs.
   Response: {2-digit channel number} {RET}
   • Set device select-code in High Speed Paper-Tape Reader driver.
   • Adjust LWAM to include driver.
   • Adjust link for interpreter.
   Response: {RET}
   • The link for the PTAPE command is a STOP handler. Programs can be loaded from the TTY/console paper-tape reader via the TAPE command.
3. Query: PUNCH I/O ADDRESS?
   This is the device used by the interpreter for storing user programs via the PLIST command.
   Response: {2-digit channel number} {RET}
   • Set device select-code in punch driver.
   • Adjust LWAM to include driver.
   • Adjust link for interpreter.
   Response: {RET}
   • The punch output will go to the TTY/console.
4. Query: SYSTEM DUMP I/O ADDRESS?
   This is the device to which PBS will output the configured system in absolute-load format.
   Response: {2-digit channel number} {RET}
   • The dump output will go to the according device.
   Response: {RET}
   • The dump output will go to the TTY/console.
5. Query: CORE?
   Response: {number>8} {RET}
   • Adjust link pointers.
   • Adjust LWAM.
   • Move drivers to higher memory.
   Response: {RET}
   • Configure for 8KW.
6. Set assorted table pointers.
7. Halt the CPU.
8. When RUN is pressed, dump two segments of absolute-load data to the previousy specified dump device:
   • The I/O-package link area (low memory), and the interpreter if it has been loaded.
   • The I/O-package drivers (high-memory).

See PBS Execution Example.

Supported Language and Commands

HPBASIC is essentially adherent to the original BASIC, it does not have common alterations and extensions present in later BASICs; for example, "LET" is mandatory in assignments. Some limitations are:

• No support for string variables, though string constants for printing are supported.
• Immediate-execute mode for statements or expressions is not provided.
• Editing of an entered BASIC line is not provided, the line must be retyped. A line may be deleted by entering the line number with no statement.

There are two non-standard extensions present in HPBASIC:

• WAIT(ms): Delay for ms milli-seconds.
• CALL(id,args*): A facility to invoke user-supplied machine-code routines. Details are presented in the HPBASIC User Manual.

User commands are limited to:

• SCRATCH - Clear the program memory.
• RUN - Execute program.
• STOP - Terminate execution. Just "S" is effective.
• LIST [lineno] - List to the console device.
• PLIST - List to the paper-tape punch device (may be the console device if the I/O system was configured so). Leader and trailer nuls are included.
• TAPE - Load a program from the console device. (Note: no LF echoed.)
• PTAPE - Load from the high-speed paper-tape photo-reader if present.

Input-line editing is also limited:

• _ : (underscore) delete previous character. Repeat to delete multiple characters.
• ~ : Delete line.
• } : Delete line.
• ESC : Delete line.
• CR : Terminate line & enter it.
• LF, NUL, DEL, CTL-B, CTL-C : Ignored.

Using HPBASIC

Loading Programs

For the modern context of a simulated teletype or paper-tape reader, this flow control requirement can present a difficulty - even low bit rates (150 or even lower) and two stop bits is insufficient in providing enough time for line processing. Adding nulls after the EOL is not adequate due to the way the 12531B/C/D interfaces work - when the interpeter starts a read part way into transmission of a null character a bad character may be read, as the 12531 is not edge-triggered on the start bit. Explicit time delays after EOL, unless longer than may be desirable, may not work with USB-serial interfaces due to bufferring in the interface. If the console simulator supports hardware flow-control the READ-COMMAND signal from the 12531 might be adapted to RS-232 levels to provide flow-control.

The interpreter however, does provide an opportunity for character-oriented flow control. During normally typed input, the interpreter starts processing an input line after receiving the CR from the console, but does not output the echo LF until after completing that processing. SCOMM again, provides a facility to support this character stop-start control of transmission, via the sflow command. This is not a perfect soultion however, in that if there is an error in the source code, the consequent returned error message will confuse and may hang SCOMM. Note: When using this method, do not use the interpreter TAPE command, it does not echo an LF, simply let the console-host transmit to the interpreter at the 'prompt' level. [See: "Pocket Guide to HP Computers", page BASIC A-1].

Saving Programs

See Restarting Example.

Some Simple Programs

A few programs compatible with HPBASIC in 8KW.

• PI: Derive pi to the resolution of the native capability of the executing system. Short and simple, good as an initial test of the system.
• LANDER2: A version of the famous Lunar Lander game.
• TAXMAN: A factoring game against the computer. This program is just a few bytes short of filling the program memory in an 8KW HPBASIC system.
• PRIMES: Print prime numbers from 1 to 200.
• PFACTORS: Derive the prime factors of a number in the range 1 to 32767.
• MORTGAGE
• MORT2
• LOWPASS: Calculate component values for a low pass filter.