Please note that not all the port functions on the TI-82 are known yet.

Known ports on the TI-82
Number	Name	Read/Write
0	Link Port	R/W
1	Keyboard	R/W
2	Select rom page	R/W
3	Status	R/W
4	Interrupt control	W
10	Display controller (control port)	R/W
11	Display controller (data port)	R/W

This instruction gets input (one byte) from a port and stores the result a register. There are 2 possibilities: either you give the number of the port directly, or you store the number of the port in C. In the last case, you can store the incoming data to whatever register you want (ABCDEHL). In the first case however, you can only store to the A register. Some examples will make this clear:

Good examples:
 IN	A,(2)
 IN	A,(11)
 IN	C,(C)
 IN	A,(C)
 IN	H,(C)
Bad examples:
 IN	(HL),(3)
 IN	C,(2)
 IN	F,(C)
 IN	(IX+2),(C)
 

Both instructions (indirect and direct) take the same amount of bytes (2), but the direct way (without using the C register) is slightly faster (1 T-state).

This instruction writes one byte of output to a specific port. The arguments are the same as with the IN instruction. This means that if you point to the port directly (using its number), you can only write data from the A register. If you point to the port indirectly (using the C register), you can write data from any CPU register (ABCDEHL).

Examples:

Good Examples:
 OUT	(3),A
 OUT	(C),B
 OUT	(C),A
Bad Examples:
 OUT	(4),D
 OUT	(C),R
 OUT	(C),(HL)
 

Both instructions (indirect and direct) take the same amount of bytes (2), but the direct way (without using the C register) is slightly faster (1 T-state).

Port Functions
Port	Function
0	link port Write: Write $C0: white wire positive, red wire positive Write $D4: white wire positive, red wire negative Write $E8: white wire negative, red wire positive Write $FC: white wire negative, red wire negative Read: bit 1 set: White wire is positive, but circuit is open bit 1 res: White wire negative, or positive with electrons flowing bit 0 set: Red wire is positibe, but circuit is open bit 0 res: Red wire negative, or positive with electrons flowing
1	Keyboard port Write: A byte with one bit set to mask out several keys bit 6: Y= WINDOW ZOOM TRACE GRAPH 2ND MODE DEL bit 5: STO> LN LOG X^2 X^-1 MATH ALPHA bit 4: 0 1 4 7 , SIN MATRX x,t,o bit 3: . 2 5 8 ( COS PRGM STAT bit 2: (-) 3 6 9 ) TAN VARS bit 1: ENTER + - * / ^ CLEAR bit 0: UP DOWN LEFT RIGHT Read: A byte with bytes set according to the keys from the mask that were pressed. bit 7: ALPHA x,t,o DEL STAT bit 6: MATH MATRX PRGM VARS CLEAR MODE bit 5: X^-1 SIN COS TAN ^ bit 4: X^2 , ( ) / Y= bit 3: LOG 7 8 9 * WINDOW UP bit 2: LN 4 5 6 - ZOOM RIGHT bit 1: STO> 1 2 3 + TRACE LEFT bit 0: 0 . (-) ENTER GRAPH DOWN
2	Set rom page Write: A byte of the format %10001xxx where xxx is the number of the rompage in binary format (0 to 7).
3	Status It's better not use this one, there's not enough information about it right now.
4	Interrupt Control Used for turboing the calculars interrupts. This doesn't make the calculator faster, but some people might get that impression because of the faster handling of keypresses and the fast blinking of the cursor (this is a result from the faster interrupts). Write %00010110 : Normal interrupts %00010100 : Faster interrupts %00010010 : Even faster interrupts %00010000 : The fastest interrupts
10	Display controller control port Note: Before all write operations to the display controller (port 10 or 11), you need to call DISP_DELAY or $7F3. If you don't do this, the controller might not execute the command written to it or even execute something else. Write
11	Display controller data port