Spectrum +3

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Contents

Specifications

Memory map

Hardware

Parts list

Active components.

Location Description Amstrad part no.
IC1 Gate Array 40077 40077
IC2 Z80A CPU 40080
IC3-6 64K x 4 D.RAM 173001
IC7 256K ROM VERSION 173002
IC8 256K ROM VERSION 2 173003
IC9 TEA2000 172048
IC10 MC1376 172049
IC11 AY-3-8912A 40001
IC12 MC 1488 QUAD RS232 DRIVER 172039
IC13 MC 1489 QUAD RS232 REC 172038
IC14 74LS273 74HCT273 173004
IC15 74HCT04 40005/A
IC16 765 Floppy Disk Controller 40018
IC17 SED 9420 171034
IC18 74HCT04 173008
IC19 74HC14 171033
IC20 74HCT04 40008
TR1 TRBC3083/BC558B 172032
TR2-5 TRBC239B/BC549B 50008
Xl Crystal 35.4690MHz 172067
X2 16.000MHz Ceramic Resonator 173013
X3 6MHz Ceramic Resonator 173011
M1 UM1233 Modulator UHF 172020

pinouts

Tape/sound

Stereo jack 3.5mm.png

Pin Desc
1 Gnd.
2 Audio in (ear)
3 Audio out (mic)

TV

RCAPhono.png

Pin Desc
1 Signal ground
2 UHF video signal

RGB/Peritel

DIN8.png

Note that unlike the +2 socket, the BRIGHT signal is merged in. This means making a SCART lead is very simple.

Pin Desc Electrical Scart notes
1 +12V +12V connect to "Function Switching" pin
2 Ground 0v Connect to Audio, Blue,Green, Red, Video grounds.
3 Audio out 200mV Connect to Audio left and right.
4 Composite Sync 0.48v Connect directly to Video In
5 +12V +12V Leave unconnected
6 Green 1.67V Connect to GREEN via a 330 ohm resistor
7 Red 1.67V Connect to RED via a 330 ohm resistor
8 Blue 1.67V Connect to BLUE via a 330 ohm resistor

Aux

DBS6312.png

Pin i/o AY-3-8912 Reg 16 bit
1 Ground pin n/a
2 out 0
3 in 4
4 out 1
5 in 5
6 +12v N/a

RS232/MIDI

DBS6312.png

Pin RS232 MIDI
1 Ground Return
2 TxD not used
3 RxD Not used
4 DTR Not used
5 CTS Data out
6 +12v not used

Expansion bus

Note, this pinout differs significantly from previous models, specifically in its provision of RomCS.

it also exposes some Disk signals, possibly for a possible disk expansion for the +2A.

2x28WayEdgeConnector.png

Pin Top Bottom
1 A15 A14
2 A13 A12
3 D7 +5V
4 Rom1 /OE [1] n/c [1]
Key
5 D0 0v
6 D1 0v
7 D2 Clk
8 D6 A0
9 D5 A1
10 D3 A2
11 D4 A3
12 /Int n/c [1]
13 /NMI 0V
14 /Halt Rom2 /OE [1]
15 /MReq Disk /RD [1]
16 /IORQ Disk /WR [1]
17 /RD /Motor on [1]
18 /WR /BusRQ
19 N/C [1] /Reset
20 /Wait A7
21 +12V A6
22 -12V A5
23 /M1 A4
24 /Rfsh n/c [1]
25 A8 /BusAk
26 A10 A9
27 Reset [1] A11
  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 This pin differs from the Spectrum 48 and 128 versions of the edge connector

Power

DIN6.png

This also applies to the +2a, although the current requirement for +12v is reduced to 200mA as its not powering a disk drive.

All the logic uses +5v. The +- 12v is used for the RS232 drivers and the disk drive. Powering the +2a without these voltages is possible, although the RS232 port wont work.

Pin Desc Electrical
1 +5V 2A between both pins
2 +5V 2A between both pins
3 +12V 700mA between both pins (200mA for +2a)
4 +12V 700mA between both pins (200mA for +2a)
5 -12V 50mA
6 Ground Ground

Printer

2x17WayEdgeConnector.png

Pin Top Bottom
1 /Strobe Ground
2 D0 Ground
3 D1 Ground
4 D2 Ground
Key
5 D3 Ground
6 D4 Ground
7 D5 Ground
8 D6 Ground
9 D7 n/c
10 n/c Ground
11 Busy n/c
12 n/c n/c
13 n/c n/c
14 Ground n/c
15 n/c Ground
16 Ground n/c
17 n/c n/c

Drive B

2x17WayEdgeConnectorkey2-3.png

Pin Top Bottom
1 Ground /Ready
2 Ground /Side 1
Key
3 Ground /Read data
4 Ground /Write protect
5 Ground /Track 0
6 Ground /Write gate
7 Ground /Write data
8 Ground /Step
9 Ground /Direction
10 Ground /Motor on
11 Ground n/c
12 Ground /Drive1
13 Ground n/c
14 Ground /Index
15 Ground n/c
16 Ground n/c
17 Ground n/c

Joystick

The joystick pinout for the Spectrum +2, +2a and +3 is different than the Atari standard, although it shares the same connector. Plugging in Atari joysticks wont Hurt, it just wont work.

     1 2 3 4 5
  |-------------|
   \ o o o o o /
    \ o o o o /
     ---------
      6 7 8 9
Pinout
Pin # Joystick
1 N/c
2 common
3 n/c
4 /fire
5 /up
6 /right
7 left
8 common
9 down

Note that all data pins are active low, although lack pull-ups.

Mods

Disk swap mod

This mod is a simple mod to allow the swapping of Drive A and Drive B.

It relies on having a socketed uPD765..

All it is is a switch that swaps in an inverter into the Drive select signal that runs from the uPD765 to the 74HC04 that buffers the lines to the disk drive.

THere are four wires to the board, VCC and 0v go to appropriate power lines, The input line goes to the Upd765 pin 29 (Unit select 0) This pin is bent up. The output line goes to pin1 of the 74HC04..