Sinclair Cambridge - TMS0801 Emulator

Current Address

000

Flags	A	9	8	7	6	5	4	3	2	1	0
A	○	○	○	○	○	○	○	○	○	○	○
B	○	○	○	○	○	○	○	○	○	○	○

Register	Mantissa									Exponent
A	0	0	0	0	0	0	0	0	0	0	0
B	0	0	0	0	0	0	0	0	0	0	0
C	0	0	0	0	0	0	0	0	0	0	0

Sinclair Cambridge
Prototype Model

C	CE

7	8	9	÷

4	5	6	×

1	2	3	−

•	0	=	+

What is this?

This is an emulation of the Sinclair Cambridge Type 2 (Prototype Model), introduced in 1973, it was the cheapest pocket calculator of the time, built with a TMS-0801, one of Texas Instrument's first "calculators on a chip".

I extracted the ROM directly off of a die of the chip. You can read more about that here.

Programmable Logic Array (PLA)

Texas Instruments was unique for including multple PLAs into their chip. This was like microcode added in addition to the ROM.

This emulator reads the PLA too. Here is the ALU PLA, which sets which opcode does which math operation:

Opcode	>>	<<	−	Hex	C	A	B	K	A=	C=	B=	A⇄B	Wait	Result
00						✓	✓		✓					A = A + B
01						✓		✓	✓					A = A + K
02						✓		✓		✓				C = A + K
03							✓		✓					A = B
04							✓			✓				C = B
05					✓			✓	✓					A = C + K
06					✓			✓			✓			B = C + K
07			✓			✓	✓		✓					A = A - B
08			✓			✓	✓			✓				C = A - B
09			✓			✓		✓	✓					A = A - K
10			✓		✓		✓			✓				C = C - B
11			✓		✓			✓		✓				C = C - K
12			✓			✓	✓							A - B
13			✓	✓		✓		✓						Hex A - K
14			✓		✓		✓							C - B
15			✓		✓			✓						C - K
16								✓	✓					A = K
17								✓			✓			B = K
18								✓		✓				C = K
19												✓		A⇄B
20		✓		✓		✓			✓					A = A << 4
21		✓		✓			✓				✓			B = B << 4
22		✓		✓	✓					✓				C = C << 4
23	✓								✓					A = A >> 4
24	✓										✓			B = B >> 4
25	✓									✓				C = C >> 4
26						✓		✓	✓				✓	Wait A = A + K
27				✓		✓		✓	✓					Hex A = A + K
28			✓	✓		✓		✓	✓					Hex A = A - K
29					✓			✓		✓				C = C + K
30														No Operation
31														No Operation
Opcode	>>	<<	−	Hex	C	A	B	K	A=	C=	B=	A⇄B	Wait	Result

When the result isn't being saved anywhere, then only the carry/borrow flag is set.

Hex means the operation is hexadecimal. No hex means the operation is decimal (BCD).

Source code

Acknowledgments / Resources

This emulation would be lacking without the resources below: