Psion Series 3a
 | |
| A Psion Series 3a | |
| Specifications | |
|---|---|
| Developer | Psion PLC |
| Manufacturer | Psion PLC |
| Type | Clamshell palmtop / PDA |
| Released | 1993 |
| Discontinued | 1998 |
| Intro price | From £269 (256 KB, 1993) |
| CPU | NEC V30H @ 7.68 MHz, integrated into Psion's ASIC9 |
| Memory | 1 MB ROM; 256 KB, 512 KB, 1 MB or 2 MB RAM |
| Storage | Two internal Solid State Disk (SSD) slots |
| Display | 480 × 160 monochrome LCD with a grey plane |
| Sound | Membrane speaker, built-in microphone, 12-bit sound recording |
| Dimensions | 165 mm × 85 mm × 22 mm |
| Weight | 275 g including batteries |
| OS / Firmware | EPOC16 (SIBO), with OPL |
| Predecessor | Psion Series 3 |
| Successor | Psion Series 3c |
| Model no. | Also sold as the Psion Series 3aR (Russian) and the Acorn Pocket Book II |
The Psion Series 3a is the 1993 development of the Psion Series 3, and the machine most people mean when they say "Psion 3". It doubled the processor speed, gave the screen 67 % more area and a grey plane, and added sound recording — while keeping the same case, the same two AA cells and the same 80-hour battery life.[1]
Internally it is the first machine to use ASIC9, the Psion custom chip that folds the V30H processor and the earlier ASIC1 and ASIC2 support chips into one device.[2]
Hardware
[edit | edit source]| Item | Specification |
|---|---|
| Processor | NEC V30H (80C86-compatible, 16-bit) at 7.68 MHz, inside Psion's ASIC9 |
| ROM | 1 MB |
| RAM | 256 KB or 512 KB at launch; 1 MB and 2 MB added in 1995 |
| Display | 480 × 160 monochrome LCD with an additional grey plane. No backlight. |
| Keyboard | 58-key QWERTY plus 8 reprogrammable application buttons |
| Sound | Membrane speaker, built-in microphone, 12-bit sound recording (uncompressed, about 8 KB per second) |
| Storage | Two internal SSD slots (RAM, Flash I and Flash II packs) |
| Serial | RS-232C at 19,200 bit/s via the 3Link pod |
| Main power | 2 × AA cells, about 80 hours |
| Backup power | CR1620 lithium coin cell |
| External power | 9 V, 150 mA |
| Size and weight | 165 × 85 × 22 mm, 275 g with batteries |
ASIC9
[edit | edit source]The Series 3 and its MC and HC siblings used three chips — the V30H, ASIC1 (the system controller, about 4300 gates in a 100-pin flat pack) and ASIC2 (the clock, keyboard, buzzer, SSD and power-supply interface, about 2200 gates in an 80-pin flat pack). ASIC9 integrates all three.[2]
That integration bought several things that matter when you are working on a 3a:[2]
- Double the clock speed. The Series 3 was held to 3.84 MHz because ASIC1 assembled each 16-bit word from two 8-bit ROM reads, needing about 250 ns ROM. ASIC9 does 16-bit accesses, so the same 200 ns mask ROM supports 7.68 MHz.
- Bank-switched memory beyond the V30H's 1 MB limit, through four page registers PSEL0–PSEL3, giving a 16 MB RAM space and a 16 MB ROM space.
- A hardware 32-bit real-time clock clocked at 1 Hz. On the earlier ASIC1/ASIC2 machines the CPU had to wake periodically to keep time, and if it could not start — no main batteries — the time was lost. The 3a keeps time independently.
- Hardware wait on pack access, which stops the CPU clock automatically when the serial controller is busy instead of polling for it.
- Switch-on from the membrane key pads, not just the on key.
- Improved grey scale: the second video map became an attribute map that dims only set pixels.
Power rails
[edit | edit source]SIBO machines run four power states — standby, backup, idle and operating — and the supply generates a set of named rails. Knowing what each does turns a dead machine into a traceable fault.[2]
| Rail | Purpose | Notes |
|---|---|---|
| Vcc1 | ASIC9 and all the memory — present in every state | Nominally 3.3 V on ASIC9 machines. Current-limited to a few hundred microamps in standby. Powered from the backup cell in the backup state. |
| Vcc2 | The processor and anything that can shut down | Fixed at 5 V even in a 3.3 V system. Off in standby, on automatically in idle or operating. |
| Vcc3 | The LCD module and its display drivers | Software switchable, 5 V or 3.3 V |
| Vcc5 | The 5 V pin on the external SSD slots | Software switchable |
| Vee1 | LCD bias — the contrast rail | Software switchable negative rail from a flyback converter. Contrast is set by a DAC in software, not by a potentiometer. |
| Vh | +16 V programming voltage for Flash SSDs | Software switchable flyback converter. Needed to write and format Flash packs — not to read them. |
Keyboard, buzzer and NMI
[edit | edit source]The keyboard is a matrix scanned by driving each column high in turn and reading the rows; the interface supports up to 16 rows × 12 columns, though 8 × 12 is normal.[2]
A watchdog counts up at 4 Hz and raises an NMI if it is not reset — about 0.75 seconds with interrupts disabled. NMIs are also generated by power-fail and by the SSD and expansion-port door microswitches.[2] That last point explains why door switches matter so much on these machines.
Inside
[edit | edit source]
The mainboard carries the large square Psion custom ASIC on the left, the ROM at the far right, and the SRAM devices inboard of the ROM. A 256 KB machine has two SRAMs fitted and spare solder pads for two more — which is what makes the 512 KB upgrade possible.[4]
Fitting two more SRAMs takes a 256 KB machine to 512 KB. The original devices were Sony parts; at least one attempt with Hitachi 628128 devices produced a "Memory corruption" message, which suggests the substitute was not compatible.[4]
Variants
[edit | edit source]- Psion Series 3aR — a Russian-market machine with Russian software in ROM. All other Series 3 models shipped with English software in ROM and were localised by installing software.[1]
- Acorn Pocket Book II — Acorn's rebadged 3a for schools, in 256 KB, 512 KB and 1 MB versions. Agenda was renamed Schedule and a Plotter graphing application was added.[1]
Solid State Disks
[edit | edit source]The two bays take Psion SSD packs, in two families:[1]
- RAM SSDs need their own button cell to hold data, but can be rewritten freely.
- Flash SSDs (Flash I and Flash II) need no cell and were cheaper per megabyte, but space from deleted or modified files is not reclaimed until the whole pack is reformatted — every change writes a new copy of the file into the remaining space.
That makes RAM packs the better choice for data that changes often, and Flash packs the better choice for archives.
Known problems
[edit | edit source]The Series 3 clamshell has three documented weak points, all of which the Psion Series 3a Troubleshooting Guide covers in detail:[1]
- Breakage of any of the four hinges
- Loss of function in the button bar between the two halves of the clam
- Deterioration of the cable linking the keyboard half to the screen, producing vertical lines on the display
General maintenance
[edit | edit source]Batteries, the battery lead, the SSD slots and how you open the lid are what determine whether a 3a survives. See the Psion Series 3a General Maintenance guide.
Troubleshooting
[edit | edit source]See the Psion Series 3a Troubleshooting Guide.
Hinge repair
[edit | edit source]All four hinges can be repaired, and the procedure is documented step by step. See the Psion Series 3a Hinge Repair guide.
See also
[edit | edit source]- Psion Series 3 · Psion Series 3c · Psion Series 3mx · Psion Siena
- Psion Series 5 — the 32-bit successor generation
- Battery Refurbishment
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "Psion Series 3", Wikipedia. Source for the model history and dates, screen resolutions, RAM options, the 1995 revision, the 3aR and Acorn Pocket Book variants, the DTMF dialling feature, the SSD bay arrangement, and the documented hinge, button-bar and screen-cable problems.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Psion PLC, SIBO Hardware Reference, version 2.10, 3 February 1995, published in the Psion Documentation Project. Source for the SIBO architecture, ASIC1/ASIC2/ASIC9, the memory decoding and bank switching, the interrupt allocation, the keyboard and buzzer interfaces, the watchdog, the NMI sources, the power states and every supply rail described on this page.
- ↑ "Psion specifications", netogram.com. Source for the comparative specification figures for the Series 3, 3a, 3c and Siena, including ROM sizes, keyboard layouts, serial speeds, external power requirements and weights.
- ↑ 4.0 4.1 David Kimberlin-Wyer, "Psion Series 3a Memory Upgrade", primrosebank.net. Source for the 18-step disassembly procedure, the board layout, the spare SRAM pads, the two keyboard membrane types and the reassembly caution about the bowed button bar.