Spectrum +3

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 4464	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	uPD765 Floppy Disk Controller	40018
IC17	SED 9420	171034
IC18	74HCT04	173008
IC19	74HC14	171033
IC20	74HCT04	40008
TR1	BC308B/BC558B	172032
TR2-5	BC239B/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

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

TV

Pin	Desc
1	Signal ground
2	UHF video signal

RGB/Peritel

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

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

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.

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

↑ ^1.0 ^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

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

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

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..

Schematic
Board mounted to the front
Solder locations to the uPD765 and the 74HC04

[diff-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

[1]

Spectrum +3

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