The 9845B/T

The 9845B workstation had been designed as an integrated desktop solution with keyboard, CRT monitor, thermal printer and two cartridge tape drives in one single system.

The whole design, although highly integrated, still is quite serviceable. Every component can be accessed with only a few steps.

Due to the integrated design only a few cables are needed. All connections have been positioned at the back of the system, so no cables are visible to the user and everything looks quite tidy. The 9845 provides a connector to AC power and four I/O connectors for expansions like interface modules.

Because of the high number of components and the resulting high power consumption, a cooling flow of air is guided from the front through the whole system and exhausted by two fans mounted in the back of the system. The thermal design made it possible to pack all the boards tightly together.

The standard monitor is passively cooled by convection.

The 9845B keyboard includes a standard Selectric-type alphanumeric key block, a separated numeric key block, a number of special function keys which can be assigned by the user to any key sequence macros, and several special keys mainly for editing and system control.

All keys have a high-quality mechanism suitable for fast and comfortable typing. Keycaps are the same as for the 9825 and 9835, however the switch mechanism had been enhanced. I do not own a single 9845 keyboard with non-working keys.

The 9845 could either be ordered as 9845B base system with single cartridge tape drive and without printer and then upgraded as needed, or as complete system with two cartridge tape drives an thermal printer already installed.

In the middle between the alphanumeric key block and the numeric key block is a row of frequently used system control keys. While the normal PC's Enter key combines several functions like "input done/continue", "store" or "execute", the 9845B has one key for each of these functions. Also there are individual keys for running or pausing a program.

The special function keys above can be either used for functions defined by a program, or can be user assigned with arbitrary key sequence macros.

The 9845B could be ordered with a built-in, 80 character wide thermal printer. The printer can be fed with any standard fax thermal paper on paper roll.

The printer is pretty fast (up to eight pages per minute), and can also print 560 pixel wide dot matrix graphics such as screen dumps. If the paper has page index holes (for positioning at perforation), the 9845 recognizes them.

Two keys can be used to advance paper either by one single line or up to the start of the next page. After finishing printing, the paper can be simply cut off.

The cartridge tape system had been quite sophisticated for the time. It was extremely fast (at least compared to compact cassette solutions) and (30 years ago) also quite reliable. The cartridge tapes have almost the same form factor as the more recent QIC 40/80 cartridges, and were much more handy than the 5.25" or 8" floppies of the time.

The 9845 could use a special command to save the full machine state on tape (somewhat like the suspend-to-disk function of modern systems), so that work could be continued even after powering the system off and on again.

Extensions to the operating system firmware was kept for the 9845B in ROM modules, which could be easily installed and exchanged by the user in one of the two ROM drawers. Each of the two CPUs of the 9845 had its own ROM drawer. This one is that of the PPU.

The ROM modules are fairly reliable, so one of the most frequent reasons for 9845B systems to hang up during boot - the system ROM failure - normally does not apply to the 9845A, which has all of its system ROMs in pluggable ROM modules.

Same ROM drawer (LPU), but opened. The LPU ROM drawer is in general populated with at least an I/O Option ROM and - if the graphics option is installed - the Graphics Option ROM.

Here also the Structured Programming ROM is installed (which upgrades the standard HP BASIC in a powerful high level programming language similar to Visual Basic) and the Assembly Execution and Development option ROM (which adds interactive Assembly Language development and execution environments).

9845 BASIC was quite capable, and it was almost impossible to remember all the keywords. So the 9845 provided help cards with quick information overview about all available commands. Also there were listings for all error messages and the most important operations needed to work with a 9845 system (also including the current system configuration). All cards were installed as pull-out cards below the CRT monitor and could easily be accessed each with its own tab.

When adding an option ROM for expanding the system firmware, sometimes there were stickers included which could be placed on one of the spare cards.

The brightness of the CRT monitor display can be adjusted with a small knob on the left below the CRT monitor. If you can't see output on the CRT, the first action should be to turn this control.

You also can see the latch for the CRT monitor. There is one latch on each of the legs on which the monitor is mounted. Push in both latches and you can lift up the whole CRT monitor assembly.

Compared to other systems of the time the 9845 had no interfaces to external peripherals. There is almost nothing built-in, no standard parallel or serial port, no joystick port, no external sound. The four connectors in the back of the system each represent a connection to the 9845 I/O bus, and are best comparable to the ISA or PCI expansion slots of common PCs.

In order to connect a device (or a network) to it, the appropriate expansion module or "interface" has to be plugged into one of those slots. There were interfaces for almost everything available, including a self-contained real time clock with battery back-up.

If four slots are not enough, there is a special bus extender, which provides seven I/O slots in a separate break-out box.

HP 9845 interfaces in general look much like cables with big plugs. In fact the "plug" holds all the electronics, which is needed to interface to the device at the other end of the cable.

Compared to a standard PC, the HP 9845 interfaces are essentially expansion boards which are plugged from outside to the computer case instead of being installed inside the system.

All 9845 models support all interfaces. In general, those interfaces are also compatible with the HP 9825 (most were in fact originally developed for the 9825).

Here a number of the most common interfaces is plugged into the I/O slots. Form left to right:

98035A Real Time Clock
98036A RS-232 Serial Interface
98032A GPIO Interface
98034A HP-IB Interface

The 9845 could be operated with both 110V/60Hz and 220V/50Hz AC. However it did not have a voltage auto-detect like modern switching PSU have, so it is essential to check and configure the 9845 to the right setting before connecting it to a power line.

If nothing happens when switching on a 9845 (even fans not spinning) probably the fuse has to be exchanged. But consider that there might be a reason why the fuse has blown before, which can indicated it is not safe to power on the system because the reason (e.g. a short circuit) is still there.

The 9845 uses a standard power cord to connect to the AC power source. Power consumption is 275 Watts maximum.

The power jack is part of a line filter module which is placed directly behind the rear cover.

The system without the CRT monitor is also called the "mainframe". It includes (in a highly packed way) the core components (PSU, mainboard, CPUs, memory, display logic, keyboard) and a couple of useful peripherals (thermal printer, cartridge tape drives).

The whole system may appear somewhat bulky, at least compared to other desktop systems, however one have to keep in mind that a complete printer subsystem is included.

The CRT display is a complete unit, but is not connected by a cable to the main system, but rather via connectors integrated into the two CRT monitor "legs".

This is necessary, because the HP 9845 has an "intelligent" CRT display, which means that parts of the alpha controller and the whole graphics subsystem is inside the CRT unit. Therefore lot more signals have to be provided to the CRT than just an RGB signal.

Which again means, that the CRT unit is fixed mounted and can't be adjusted to other angles of view.

In the middle is the PSU with its aluminium plate, framed by the CRT monitor legs, the I/O backplane and the printer.

All mainframe boards plug into edge connector slots in mainboard, which is mounted on the system's floor.

Note that each board is equipped with a pair of levers for extracting the boards from their slots. Also those levers denote with a color code on the PCB guidance which board has to be placed in which slot.

Although extracting gets easier with those levers, it is not recommended to use them, since they have lost their stability during the years and quickly brake off. Better try to move the boards by grabbing the board's PCB.

The board half extracted from the cage is the memory address extension board, which allows the 9845B processors to address more than one 64 kByte memory block.

Next to the LPU board there is the PPU RAM/ROM assembly. Note that here the ROM board is installed as a piggy-back PCB on the RAM/ROM assembly, replacing the original PPU ROMs which have gone defect.

The PPU RAM/ROM board holds 128 kBytes of ROM and 32 kBytes of RAM (half a memory block). The PPU RAM also functions as a character buffer for the CRT display.

The internal printer is a larger unit, which takes some space inside the 9845 mainframe. However compared to external printers, it has an overall compact design to fit inside the system.

Note the paper roller, which moves the paper. The roller itself is driven by a stepper motor over a drive belt.

The assembly which is pulled up is a 512k memory board, which is the largest memory assembly for the HP 9845. It works with both HP 9845B and HP 9845C, however needs a special ROM set in order to make the additional RAM space available for all software.

Up to three of these boards can be installed, providing the HP 9845 with 1.5 MBytes of memory - an incredible amount of RAM at a time, when the IBM PC was not yet invented on which Bill Gates once stated "no one will ever need more than 640 kBytes"...

With all cards removed from the card cage, the alpha control assembly gets visible. It holds all electronics for reading the display buffer in the PPU memory block, for working the display list stored in that buffer, and for sending a character stream to the CRT display.

Note that the board is partly hidden behind an aluminium plate which secures the left CRT display leg. Also note the two edge connectors on the botton, which connect the PPU board to the PPU's memory bus and the system I/O bus.

The 9845 was a wonder of micro electronics. Probably is was the highest integrated system at the time. Nevertheless, the system design is totally modular and service friendly.

Everything was within reach with only a few movements. The system could be operated and tested when opened.

Below the keyboard/tape drive unit are the air inlets, through which the air is drawn into the system. Originally, those inlets are armed with exchangeable air filters in order to prevent dust being moved inside the system. Those filters are made of foam and have totally desintegrated through the time.

However if you like, you can replace them with new ones.

The keyboard/tape drive unit can be fully folded so that the assemblies can easily be accessed.

The unit consists of the following assemblies:

tape cartridge drive controllers (those with the heat sinks on it, one for each drive)
tape drives (with the motor on them, again one for each drive)
keyboard logic (the board in the center)
interconnect board (below the keyboard logic and tape controllers)
key switch PCB (where the keys are mounted)

The keyboard controller board is connected with a ribbon cable to the interconnect board below, which again is connected to the rest of the system with another ribbon cable.

Those ribbon cables often cause interconnect problems. If key won't work, this goes in estimated 95% of the cases to those ribbon cables with their connectors.

There is only one single PSU in each 9845B for supplying power to all internal components. As with all other components, the PSU is a subsystems which can easily removed from the system, not even one single cable has to be detached.

The PSU gets its 150V AC input from a four-contact MATE-N-LOK connector. The input voltage has been normalized before, so that it is independent of the main power input (110 or 220V AC).

The voltages needed by the system components are provided via two edge connectors on the bottom of the PSU bay. A number of guidances assure proper alignment when installing the PSU into the system.

The PSU bay is well-shielded against the other components.

The 9845B standard power supply unit consists of five PCBs mounted to gether to one compact assembly.

The MATE-N-LOK connector in the front matches to that in the PSU bay. The yellowish WIMA epoxy capacitor next to it already has replaced the original capacitor, which is highly recommended for all epoxy capacitors used in the PSU and the line filter of a 9845.

The HP 9845 model 200 is basically a normal HP 9845B, but with a couple of enhancements:

Most obvious, there is a larger monitor which replaces the standard 98750A monitor. For 9845B systems this is a 98780A monochrome monitor, for 9845C systems this is a 98770A color monitor.

Another difference visible from outside is the (optional) light pen.

The light pen has its home on one of the monitor legs (you can chose on your own whether it should be the left or right leg since there is a detachable sleeve where the pen is put in).

The light pen can be used to point and select items on the screen. Because the light pen needs light there is a special cursor which can be used as light source for the pen sensor.

The light pen itself only includes the lense, the sensor and the trigger switch for selections. All other electronics are on a special light pen controller board inside of the monitor.

As visible on this picture, the 98780A monitor is quite bulky. In fact integration scale is not as high as that of the mainframe, since the 98780A uses the same casing as the 98770A but without own PSU and fans and with less components inside. So there is much space in the monitor, and it is not as heavy as it looks like.

The 98780A monitor already supports monochrome graphics as standard, so that there has no graphics option to be ordered separately. Also, the graphics controller already includes a fast vector generator which (since only monochrome date has to be written) draws vectors even faster than that of the 98770A color monitor.

The 9845B model 200 fans are more powerful (and noisy) than their 9845B model 100 counterparts.

The 9845B model 200 monitor is cooled by convection, there is no fan installed.

The four I/O expansion slots are identical to those of the 9845B model 100.

The light pen connects to a SUB-D connector at the back of the monitor. The connector again connects to a large light pen controller board inside of the monitor.

The signal from the light pen is compared in real time to the CRT beam position, which again is reported to the program which uses the position information e.g. for selections or drawing operations.

The new graphics capabilities, the larger screen, light pen and soft keys are not the only enhancements of the model 200. It also includes a faster LPU, which is based on a fast bit-slice design with some diskrete logic.

The new CPU does not need a heat sink any more, however is distributed over four (!) PCBs. Again HP's engineers did the magic to get this still into the volume previously occupied by the standard LPU.

The new LPU is slot-compatible with the old, so electrically they are interchangeable. However the new CPU consumes more power, so that a new PSU is needed, too.

The new PSU which provides the necessary additional power for the fast processor and the 98780A display is installed at the same place as the standard PSU before.

The test point have been replaced by a power-good sensor circuit with four LEDs. During operation, all four LEDs should be lit.

Just with the fast LPU, exchanging the old PSU against the enhanced one is just a matter of minutes and a small number of moves.

For transporting more thermal energy out of the system, the model 200 also incorporates more powerful (and significantly more noisy) fans in the mainframe.