TI99/4A

TI99/4AThe TI 99/4A was released in 1981, with a TMS-9900 CPU (first 16 bit CPU) it was the second computer Texas Instruments released using a 16-bit CPU on the market. The CPU was already used in the TI-99/4 Version but improvements where done and the TI-99/4A was born. Although it used a 16 bit CPU the internal bus works in 8 bit, which limited the computer a lot. Its ROM BASIC was very limited and very slow as was ported from the TI-99/4. Texas Instruments later released a cartridge to improve its BASIC Language with extra commands. No PEEK/POKE/CALL was available to access its ROM or writing machine code. The TI-99/4A had a vast range of peripherals such as disk drives, hard disks, and with an external large case for large expansion boards. There were 2 different case versions of the TI-994/A The US and the French/Europe Version.
TI-99/4A
$525 US Version £410 UK Version
0335504483RC1,
52141187LTA5083,
60000509LTA3183
1981
TMS-9900 16 bit CPU running at a frequency of 3.33 MHz. Although it uses a 16 bit CPU only the system ROMs and 256 bytes of scratchpad RAM is available on the 16-bit bus. The rest are on a 16 to 8 bit multiplexer which needs 2 clock cycles in order to work. Because of this in reality it reduced the frequency speed to 1.6 Mhz.
26Kb ROM containing BASIC. 16Kb expandable to 48Kb, the 16Kb of RAM is are only accessible by the TMS-9918A. As mentioned earlier due to the multiplexer and paging it slowed the machine drastically.
2 case versions, one black with aluminum frame, and one light gray plastic case. All cases have the same shape except for the third version with the power switch moved to the front. The keyboard is a standard QWERTY 48 key with special function button.
The text & graphics are generated from a TMS-9918A custom chip US Version or TMS9929A in the Europe version. The A in the custom chip was adopted in the Model No hence TI99/4A. Text Mode 32×24 with 16 colours, 256 glyph character set, and a matrix of 8×8. All character set is programmable. Since colour 0 is transparent it can be used to create holes in sprites. Text-Only Mode 40×24 with 2 colours monochrome, and characters are set with a matrix of 6×8 leaving the sides as borders. No sprites are available in this mode. Bitmap mode with a resolution of 256×192 with 16 colours and high picture resolution. Multi colour Mode 64×48 with 16 colours and a pixel block of 4×4. The chip can support up to 32 sprites.
TMS 9919 Audio generator, with three channels of sound and one of white noise. Sound is Mono, with a full range of frequencies to choose.
1 x Cartridge port for expansion of ROM, Basic, Games etc.
1 x Expansion,
1 x Composite Video to connect a monitor or the supplied TV Modulator.
1 x Tape Recorder which could accept two tape decks with a rate of 450 Bps.
1 x Joystick port like the tape deck it accepts two joysticks thru a single connector.
External power supply with voltages 16V AC and 8V AC
Dimensions 380 mm x 255 mm x 60 mm (W x L x H) Weight 2.15 kg.
More than 2.5 million units worldwide.

The club owns three models Boxed with all related manuals (Read this first!, Beginners Basic, User’s Reference guide, Reference card,Video Modulator manual, Addendum and Warranty booklet.). They are all in perfect working condition.

Cassette I/O Port

9-Pin d-sub
at the back of computer
Pin Name Dir Desc
1 CS1 IN Motor Control Cass1
2 CS1 N/A Motor Control Cass1
3 GND N/A Ground
4 SOUT OUT Sound Out
5 ROUT OUT Record Output
6 CS2 IN Motor Control Cass2
7 CS2 N/A Motor Control Cass2
8 AIN IN Audio In
9 AGND N/A Audio Ground
 

 

Joystick Port

9-Pin d-sub
at the back of computer
Pin Name Dir Desc
1 NC N/A No Connection
2 JS 2 OUT Joystick Select 2
3 JS K0 IN Joystick UP
4 JS K4 IN Joystick FIRE
5 JS K3 IN Joystick LEFT
6 NC N/A No Connection
7 JS 1 OUT Joystick Select 1
8 JS K1 IN Joystick DOWN
9 JS K2 IN Joystick RIGHT
 

 

Power

4 Pin Male connector
at the back of computer
Pin Name Dir Desc
1 16V~ IN 16V AC 1.6A
2 16V~ IN 16V AC 1.6A
3 8V~ IN 8V AC 0.15A
4 8V~ IN 8V AC 0.15A
 

 

Video Port NTSC

5 Pin Din 180
Pin Name Dir Desc
1 +12V OUT +12V
2 GND N/A Ground
3 SOUND OUT Sound Out
4 COMP OUT Comp Video
5 SGND N/A Signal Ground
 

 

Video Port PAL

6 Pin DIN (DIN45322) Female at the Computer
Pin Name Dir Desc
1 +12V OUT +12V
2 COMP OUT Comp Video
3 R-Y OUT R-Y
4 B-Y OUT B-Y
5 SOUND OUT Sound Out
6 SGND N/A Signal Ground
 

 

Cartridge Port

Cartridge Connector 36 Pin
Pin Name Dir Desc
1 RES IN Reset SYS (Active High)
2 GND N/A Ground
3 D7 IN/ OUT Data Bit 7
4 /CRU CLK OUT INV TMS9900
5 D6 IN/ OUT Data Bit 6
6 CRUIN IN CRU Input TMS9900
7 D5 IN/ OUT Data Bit 5
8 A15 OUT Address Bus 15
9 D4 IN/ OUT Data Bit 4
10 A13 OUT Address Bus 13
11 D3 IN/ OUT Data Bit 3
12 A12 OUT Address Bus 12
13 D2 IN/ OUT Data Bit 2
14 A11 OUT Address Bus 11
15 D1 IN/ OUT Data Bit 1
16 A10 OUT Address Bus 10
17 D0 IN/ OUT Data Bit 0
18 A9 OUT Address Bus 9
19 VCC OUT +5 Volts Supply
20 A8 OUT Address Bus 8
21 /GS OUT Grom Sel Active Low is addr in > 9800-9FFF.
22 A7 OUT Address Bus 7
23 A14 OUT Address Bus 14 Sel Mode: low=data / high=addr
24 A3 OUT Address Bus 3
25 DBIN OUT Active high = read mem
26 A6 OUT Address Bus 6
27 GRC OUT Grom Clock: 447.7 Khz Signal from the VPD
28 A5 OUT Address Bus 5
29 VDD OUT -5 Volts Power
30 A4 OUT Address Bus 4
31 GR IN Active High = GROM ready.
32 /WE OUT Active Low Write Enable
33 VSS OUT Digital Ground
34 /ROMG OUT Active Low when in addr >6000 – 7FFF
35 GND N/A Ground
36 GND N/A Ground
 

 

Peripheral Port

Peripheral Connector 44 Pin
Pin Name Dir Desc
1 VCC OUT +5V Supply
2 SBE OUT High if addr in >9000-94xx (Sound Port)
3 /RES OUT Active Low System Reset
4 /EXT INT IN Active Low External Inerrupt
5 A5 OUT Address Bus 5
6 A10 OUT Address Bus 10
7 A4 OUT Address Bus 4
8 A11 OUT Address Bus 11
9 DBIN OUT Active High Read Memory
10 A3 OUT Address Bus 3
11 A12 OUT Address Bus 12
12 RDY IN Active High Memory Read
13 LOAD IN Unmaskable Interrupt (=> BLWP @> FFFC)
14 A8 OUT Address Bus 8
15 A13 OUT Address Bus 13
16 A14 OUT Address Bus 14
17 A7 OUT Address Bus 7
18 A9 OUT Address Bus 9
19 A15 OUT Address Bus 15
20 A2 OUT Address  Bus 2
21 GND N/A Ground
22 /CRU CLK OUT Inversion of TMS 9900 CRU CLOCK pin
23 GND N/A Ground
24 /PHI3 OUT Inversion of Phase 3 Clock
25 GND N/A Ground
26 /WE OUT Active Low Write Enable
27 GND N/A Ground
28 /MBE OUT Active Low if Address in >4000 – 5FFF
29 A6 OUT Address Bus 6
30 A1 OUT Address Bus 1
31 A0 OUT Address Bus 0
32 /MEM EN OUT Active Low Memory Access Enable
33 CRU IN IN CRU Input bit to TMS 9900
34 D7 IN/ OUT Data Bit 7
35 D4 IN/ OUT Data Bit 4
36 D6 IN/ OUT Data Bit 6
37 D0 IN/ OUT Data Bit 0
38 D5 IN/ OUT Data Bit 5
39 D2 IN/ OUT Data Bit 2
40 D1 IN/ OUT Data Bit 1
41 IAQ OUT Interrupt Acnow TMS9900
42 D3 IN/ OUT Data Bit 3
43 VDD OUT -5 Volts Power Supply
44 AUD IN IN To Sound Gen Audio In