Difference between revisions of "83:Ports:00"
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'''Port Number:''' 00h | '''Port Number:''' 00h | ||
| − | '''Function:''' Link | + | '''Function:''' Link port and Rom page swapping |
| − | This port controls the calculator's serial link port. | + | This port has two functions. It controls the calculator's serial link port and together with [[83:Ports:02]], the ROM page that is swapped into 4000h-7FFFh. |
=== Read Values === | === Read Values === | ||
* Bit 0 and 1: The inverse of the values output to the link port. | * Bit 0 and 1: The inverse of the values output to the link port. | ||
* Bit 2 and 3: These two bits indicate the state of the link port's two lines. A 1 bit indicates a high line, and a 0 bit indicates a low line. When idle (no transfer in progress, no cable plugged in, etc), both lines are usually high (1). When a cable is connected on both ends, a line reads high if and only if both ends have set the line high. The line will read low if either calculator sets it low. | * Bit 2 and 3: These two bits indicate the state of the link port's two lines. A 1 bit indicates a high line, and a 0 bit indicates a low line. When idle (no transfer in progress, no cable plugged in, etc), both lines are usually high (1). When a cable is connected on both ends, a line reads high if and only if both ends have set the line high. The line will read low if either calculator sets it low. | ||
| − | * Bit 4: Bit 3 of the current ROM page | + | * Bit 4: Bit 3 of the current ROM page. See also [[83:Ports:02]]. |
* Bit 5-7: Zero | * Bit 5-7: Zero | ||
=== Write Values === | === Write Values === | ||
* Bit 0 and 1: The low 2 bits indicate what state the lines should be put into. A 1 bit will pull the line low. A 0 bit will stop holding the line low (allowing it to go high if the other calculator is not holding it low). | * Bit 0 and 1: The low 2 bits indicate what state the lines should be put into. A 1 bit will pull the line low. A 0 bit will stop holding the line low (allowing it to go high if the other calculator is not holding it low). | ||
| − | * Bit 4: Bit 3 of the current ROM page | + | * Bit 4: Bit 3 of the current ROM page. See also [[83:Ports:02]]. |
| − | * Bit 6 and 7: These bits should be 1 for unknown reasons | + | * Bit 6 and 7: These bits should be 1 for unknown reasons. |
| − | + | ||
== Comments == | == Comments == | ||
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Transferring an entire byte requires you to implement some form of protocol. Examples include TI's official linking protocol, and [http://www.ticalc.org/archives/files/fileinfo/277/27718.html Michael Vincent's TachyonLink protocol]. | Transferring an entire byte requires you to implement some form of protocol. Examples include TI's official linking protocol, and [http://www.ticalc.org/archives/files/fileinfo/277/27718.html Michael Vincent's TachyonLink protocol]. | ||
| − | + | Other useful information on linking in general: | |
| − | * [http://www.ticalc.org/archives/files/fileinfo/247/24750.html TI Link Protocol & File Format Guide] | + | * [http://www.ticalc.org/archives/files/fileinfo/247/24750.html TI Link Protocol & File Format Guide] |
| − | * [http://www.ticalc.org/archives/files/fileinfo/294/29418.html Ti-83 Link Port Tutorial] | + | * [http://www.ticalc.org/archives/files/fileinfo/294/29418.html Ti-83 Link Port Tutorial] |
| − | + | ||
== Example == | == Example == | ||
=== Sending/Setting === | === Sending/Setting === | ||
| − | < | + | <nowiki>ld a,$D0 ; Set both lines high |
out (0),a | out (0),a | ||
| Line 45: | Line 43: | ||
ld a,$D3 ; Set both low | ld a,$D3 ; Set both low | ||
| − | out (0),a</ | + | out (0),a</nowiki> |
=== Receiving/Reading === | === Receiving/Reading === | ||
| − | < | + | <nowiki>in a,(0) ; Get the link port value |
bit 2,a ; Check tip | bit 2,a ; Check tip | ||
| Line 56: | Line 54: | ||
bit 3,a ; Check ring | bit 3,a ; Check ring | ||
jr z,ring_low | jr z,ring_low | ||
| − | jr nz,ring_high</ | + | jr nz,ring_high</nowiki> |
Revision as of 05:40, 30 March 2005
Contents
Synopsis
Port Number: 00h
Function: Link port and Rom page swapping
This port has two functions. It controls the calculator's serial link port and together with 83:Ports:02, the ROM page that is swapped into 4000h-7FFFh.
Read Values
- Bit 0 and 1: The inverse of the values output to the link port.
- Bit 2 and 3: These two bits indicate the state of the link port's two lines. A 1 bit indicates a high line, and a 0 bit indicates a low line. When idle (no transfer in progress, no cable plugged in, etc), both lines are usually high (1). When a cable is connected on both ends, a line reads high if and only if both ends have set the line high. The line will read low if either calculator sets it low.
- Bit 4: Bit 3 of the current ROM page. See also 83:Ports:02.
- Bit 5-7: Zero
Write Values
- Bit 0 and 1: The low 2 bits indicate what state the lines should be put into. A 1 bit will pull the line low. A 0 bit will stop holding the line low (allowing it to go high if the other calculator is not holding it low).
- Bit 4: Bit 3 of the current ROM page. See also 83:Ports:02.
- Bit 6 and 7: These bits should be 1 for unknown reasons.
Comments
Ti-OS interference
One thing to keep in mind when writing link port related software is that the Ti-OS checks for silent transfers in the background. When two calculators are connected and one pulls a line low, the other calculator will respond by pulling the other line low to acknowledge that it has received a bit. This phenomenon is known to cause severe headaches for programmers who attempt to write synchronization routines :). It's unclear if this is only when the other calculator is in the homescreen, or if it is part of the default interrupt routine at $0038.
Data transfer
Transferring an entire byte requires you to implement some form of protocol. Examples include TI's official linking protocol, and Michael Vincent's TachyonLink protocol.
Other useful information on linking in general:
Example
Sending/Setting
ld a,$D0 ; Set both lines high out (0),a ld a,$D2 ; Set tip high, ring low out (0),a ld a,$D1 ; Set tip low, ring high out (0),a ld a,$D3 ; Set both low out (0),a
Receiving/Reading
in a,(0) ; Get the link port value bit 2,a ; Check tip jr z,tip_low jr nz,tip_high bit 3,a ; Check ring jr z,ring_low jr nz,ring_high
