ZX Spectrum 128K

ZX Spectrum 128The ZX Spectrum 128 initially codenamed Derby was a project in conjunction with the Spanish distributor Investronica to adapt the ZX Spectrum+ to the Spanish market, after the Spanish government imposed a special tax on all computers with 64Kb Ram or less, and a law which obliged all computers sold in Spain to support the Spanish alphabet and display messages in Spanish.

The cosmetic appearance of the unit is very similar to the ZX Spectrum+, with the exception of the large heat sink on the right side of the unit. New features were introduced such as 128Kb Ram, three sound channels, Midi, RS-232, RGB connector, and a 32Kb rom with an improved basic editor and an external keypad. The machine was simultaneously launched for the first time in September 1985 at the SIMO’85 trade show in Spain and in UK for a price tag of £179.95. In UK the unit was only available in January 1986, a decision taken by Sinclair due to the high number of Spectrum+ unsold. Since the Z80 could address only 16-bit addresses meaning only 64Kb ram can be accessed directly, Sinclair had to use an MMU chip (Memory Management Unit) for memory handling via bank switching, so the new memory will be available as eight pages of 16Kb each at the top of the address. The same technique was used for the ROM at the bottom of the address space.

The new features and advanced Ram capabilities made the machine one of the best on the market but soon other companies released more advanced machines on the market, one of these was the Commodore 128 that stated in their advert “three machines in one”. The Spectrum 128K still kept going strong as it was sold cheaper than other competitors especially in Spain which made a great hit.

ZX Spectrum 128
UK: £179.95
Boxed: A8-068039
Zilog Z80A CPU Running at a frequency of 3.5469Mhz
128Kb Ram divided into 8 bank memory of 16Kb. 32Kb Rom also paged and includes Basic and editor, The Ram is also expandable externaly to 256Kb through a 3rd party interface and used as a ram drive.
Black plastic case with the Sinclair logo and spectrum+ at the top left corner in red and 128K also in red at the bottom right corner. The keyboard is a QWERTY non-standard style. A heatsink is placed on the right hand side of the machine used for the voltage regulation cooling.
The ULA handles the display, in text mode 32 x 24 lines and graphics 256 x 192 pixels with 8 colours of 2 tones each (normal or bright).
The Sound is handled by the Yamaha AY-3-8912 with 3 Channels and 7 octaves on each channels and capable of MIDI support.
1 x Expansion Port
1 x RS232/MIDI Port
1 x RF TV Port
1 x Cassette Audio out (MIC) also used for audio RGB Monitor
1 x Cassette Audio IN (EAR)
1 x RGB Port
1 x Keypad Port
External Power Supply with a voltage of 9V DC min 2.1A
Dimensions 320mm x 150mm x 45 mm (W x L x H) Weight 950g
Sinclair sold more than 1.5 million units around the world.

The club currently owns two ZX spectrum. One system is boxed with manuals, leads and in good working condition. The other system is used as parts, since it’s completely dead. We also have the flyer that Sinclair produced for promotion. On the flyer Sinclair is comparing the ZX spectrum with a BBC micro.



3.5mm Jack Female
at the Computer

Pin Name Dir Desc
2 GND N/A Ground


Expansion Port

54 Pin Edge Connector

Pin Name Dir Desc
U1 A15 OUT Address 15
U2 A13 OUT Address 13
U3 D7 IN/
Data Bit 7
U4 N/C N/A No Conn
U5 D0 IN/
Data Bit 0
U6 D1 IN/
DataBit 1
U7 D2 IN/
Data Bit 2
U8 D6 IN/
Data Bit 6
U9 D5 IN/
Data Bit 5
U10 D3 IN/
Data Bit 3
U11 D4 IN/
Data Bit 4
U12 /INT IN Interrupt Request
U13 /NMI IN Non Mask Intr
U14 /HALT IN Request Port
U15 /MREQ IN Memory Request
U16 /IORQ IN IO Request
U17 /RD IN Read
U18 /WR IN Write
U19 -5V OUT -5V DC
U20 /WAIT IN Wait
U21 +12V OUT +12V
U22 -12V OUT -12V
U23 /M1 IN Memory 1
U24 /RFSH IN Refresh
U25 A8 OUT Address 8
U26 A10 OUT Address 10
U27 N/C N/A No Conn
L1 A14 OUT Address 14
L2 A12 OUT Address 12
L3 +5V OUT +5V DC
L4 +9V OUT +9V DC
L5 OV N/A Ground
L6 OV N/A Ground
L7 CK OUT Clock
L8 A0 OUT Address 0
L9 A1 OUT Address 1
L10 A2 OUT Address 2
L11 A3 OUT Address 3
L13 0V N/A Ground
L14 N/C N/A No Conn
L15 N/C N/A No Conn
L16 N/C N/A No Conn
L17 N/C N/A No Conn
L18 /BUSRQ IN Bus Request
L19 /RESET IN Reset
L20 A7 OUT Address 7
L21 A6 OUT Address 6
L22 A5 OUT Address 5
L23 A4 OUT Address 4
L24 /ROMCS IN Rom Channel Select
L25 /BUSACK IN Bus Acknow
L26 A9 OUT Address 9
L27 A11 OUT Address 11



3.5mm Jack Female
at the Computer

Pin Name Dir Desc
2 GND N/A Ground



35mm Jack Female
at the Computer

Pin Name Dir Desc
1 +9V IN +9C DC
2 GND N/A Ground



Phono Jack
at the Computer

Pin Name Dir Desc
2 GND N/A Ground



RJ11 Type

Pin Name Dir Desc
1 RETURN IN Return
2 N/C N/A No Conn
3 N/C N/A No Conn
4 N/C N/A No Conn
6 N/C N/A No Conn



RJ11 Type

Pin Name Dir Desc
2 REG 14 Bit 0 OUT Keypad IN
3 REG 14 Bit 4 IN Keypad OUT
4 REG 14 Bit 1 OUT Keypad IN
5 REG 14 Bit 5 IN Keypad OUT
6 +12V OUT +12V DC


RGB Monitor

8 Pin DIN (DIN45326) Female
at the Computer

Pin Name Dir Desc
1 PAL COMP OUT Composite Pal 1.2V
2 GND OUT Ground
3 LUM OUT Luminance
4 COMP SYNC OUT Composite Sync
5 VERT SYNC OUT Vertical Sync
6 GREEN OUT Green Channel
7 RED OUT Red Channel
8 BLUE OUT Blue Channel



RJ11 Type

Pin Name Dir Desc
1 GND N/A Ground
2 TXD OUT Transmit Data
3 RXD IN Receive Data
Data Terminal Ready
Clear To Send
6 +12V OUT +12V DC