Psion Series 3
 | |
| A Psion Series 3 (1991) | |
| Specifications | |
|---|---|
| Developer | Psion PLC |
| Manufacturer | Psion PLC |
| Type | Clamshell palmtop / PDA |
| Released | 1991 |
| Discontinued | Superseded by the Series 3a in 1993 |
| Intro price | £179 (128 KB), £249 (256 KB) |
| CPU | NEC V30H (80C86-compatible) @ 3.84 MHz, with Psion ASIC1 and ASIC2 |
| Memory | 128 KB or 256 KB RAM |
| Storage | Two internal Solid State Disk (SSD) slots |
| Display | 240 × 80 monochrome LCD, 97 × 39 mm |
| Sound | Piezoelectric buzzer, with DTMF tone dialling |
| Dimensions | 165 mm × 85 mm × 22 mm |
| Weight | 275 g including batteries |
| OS / Firmware | EPOC16 (SIBO), with OPL |
| Predecessor | Psion Organiser II |
| Successor | Psion Series 3a |
| Model no. | Also sold as the Acorn Pocket Book |
The Psion Series 3 of 1991 is the machine that established the Psion clamshell: a pocketable palmtop with a real keyboard, a multitasking 16-bit operating system, a built-in programming language and two removable solid-state storage bays. About 1.5 million machines were made across the whole Series 3 range.[1]
It is the slowest and lowest-resolution member of the family, and — more importantly for anyone repairing one — the only one built on the three-chip SIBO architecture rather than the integrated ASIC9 of the 3a and later.
Hardware
| Item | Specification |
|---|---|
| Processor | NEC V30H (80C86-compatible, 16-bit) at 3.84 MHz |
| System chips | Psion ASIC1 (system controller) and ASIC2 (clock, keyboard, buzzer, SSD and PSU interface) |
| RAM | 128 KB or 256 KB |
| Display | 240 × 80 monochrome LCD, 97 × 39 mm, black/white only. No grey plane, no backlight. |
| Video memory | 8-bit access at half speed |
| Sound | Piezoelectric buzzer. No sound recording. DTMF tone dialling through the speaker |
| Storage | Two internal SSD slots |
| Serial | 9600 baud via the optional link pod, with the software held in the pod's ROM |
| Main power | 2 × AA cells |
| Backup power | CR1620 lithium coin cell |
| Size and weight | 165 × 85 × 22 mm, 275 g with batteries |
Why the Series 3 is slower
The clock is held to 3.84 MHz for a specific, documented reason. ASIC1 assembles each 16-bit word from two 8-bit ROM reads, which needs ROM with about a 250 ns access time at that clock. Readily available mask ROMs of the period managed 200 ns, and that is what capped the Series 3.[3]
The 3a's ASIC9 does 16-bit accesses instead, which doubled the clock for the same ROM.[3]
The three-chip architecture
| Device | Package | Function |
|---|---|---|
| V30H | — | 80C86-compatible CPU, fully static, so the clock can be stopped at any time with no loss of state — the basis of the whole SIBO power-saving strategy |
| ASIC1 | 100-pin QFP, ~4300 gates | Bus controller, bus converter, 16-bit timer, LCD controller, memory and I/O decoding, 8-channel interrupt controller, watchdog, address and I/O protection |
| ASIC2 | 80-pin QFP, ~2200 gates | System clock oscillator, on/off control, the SIBO serial protocol controller, keyboard interface, buzzer interface and NMI generation |
Two consequences matter on the bench:
- ASIC1 stops the processor clock on a HALT instruction and holds it low until an interrupt or NMI arrives. A machine that appears frozen may simply be waiting for an interrupt that never comes.[3]
- The watchdog is a 2-bit counter clocked at 4 Hz that raises an NMI if it is not reset — roughly 0.75 seconds with interrupts disabled.[3]
Timekeeping — a Series 3-specific weakness
The ASIC1/ASIC2 machines have no hardware real-time clock. They keep time using the free-running counter, which means the CPU must wake up periodically (roughly every 8 hours) to maintain the time. If the CPU cannot start — because there are no main batteries — the time is lost.[3]
This was one of the specific limitations ASIC9 was designed to remove, and it is why a Series 3 that has been left with the AA cells out comes back with the clock wrong while a 3a does not.[3]
SIBO serial channels
ASIC2 contains an 8-channel serial protocol controller. The channel assignment is worth knowing, because it explains what shares a path with what:[3]
| Channel | Function |
|---|---|
| 0 | Power supply |
| 1–4 | SSDs |
| 5, 6 | Expansion ports |
| 7 | High-speed link |
Acorn Pocket Book
Acorn sold a rebadged Series 3 as the Acorn Pocket Book, aimed at schoolchildren rather than executives. The hardware was the same; the bundled applications differed. Agenda was omitted (supplied separately on floppy disk), and System, Word, Sheet and Data were renamed Desktop, Write, Abacus and Cards.[1]
Known problems
The Series 3 clamshell has three documented weak points:[1]
- Breakage of any of the four hinges
- Loss of function in the button bar between the two halves
- Deterioration of the screen cable, producing vertical lines
The battery lead is a fourth, and it is the one most often missed — see the Psion Series 3 Troubleshooting Guide.
General maintenance
Troubleshooting
Hinge repair
See also
- Psion Series 3a · Psion Series 3c · Psion Series 3mx · Psion Siena
- Psion Organiser II — the machine the Series 3 replaced
- Battery Refurbishment
References
- ↑ 1.0 1.1 1.2 1.3 "Psion Series 3", Wikipedia. Source for the model history and dates, prices, production numbers, screen sizes, the Acorn Pocket Book, the DTMF dialling feature, the SSD arrangement and the documented clamshell problems.
- ↑ "Psion specifications", netogram.com. Source for the comparative specification figures, video memory access mode, screen dimensions, weight and serial speed.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Psion PLC, SIBO Hardware Reference, version 2.10, 3 February 1995, in the Psion Documentation Project. Source for the SIBO architecture, ASIC1 and ASIC2 functions, the clock-speed limitation, the memory and I/O decoding, the interrupt table, the watchdog, the NMI sources, the timekeeping mechanism and the supply rails.