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In my pursuit of understanding how Game Gear communication works I wrote a couple of simple test programs that use the link protocol. They are written in C using Sverx's devkitSMS library.

G2GTest

A basic utility to send a byte and receive a byte.
Shows the status of the send and receive flags.

Up/Down to select a parameter to modify and Left/Right to change the value.

Button 1 to send the selected byte.
Button 2 to read a byte if one is waiting to be received.

https://github.com/pmckeon/G2GTest

G2GTerminal

World's simplest messaging application for the Game Gear.

Enter a message up to 60 characters using the directional pad and Button 1, Press Button 2 to send a message.

Incoming messages display in the top window.

https://github.com/pmckeon/G2GTerminal

G2GTest.PNG (9.52 KB)

G2GTerminal.PNG (13.31 KB)

G2GTest.zip (2.05 KB)

G2GTerminal.zip (2.57 KB)

Do we know which of the pins on the Gear2Gear cable hold what kind of data when the port is in "Regular" mode?

PC4 (Pin 6) is serial output and PC5 (Pin 9) is serial input. The other pins are not used in this mode but can still be driven manually as inputs or outputs.

Do we know what bitrate?

Everything is documented in the official hardware reference manual

https://segaretro.org/images/1/16/Sega_Game_Gear_Hardware_Reference_Manual.pdf

bitrate is dependant on Baud setting which is selectable between 300, 1200, 2400, 4800 (default).

Ah! Thank you!

I assumed I'd be able to find that somewhere on the SMSpower wiki but didn't think to look elsewhere afterwards (oops)

Author	Message
thatawesomeguy Joined: 25 Jul 2007 Posts: 731 Location: Melbourne, Australia	G2GTest & G2GTerminal - Game Gear communications test programs Posted: Sat Jun 26, 2021 2:21 pm
	In my pursuit of understanding how Game Gear communication works I wrote a couple of simple test programs that use the link protocol. They are written in C using Sverx's devkitSMS library. G2GTest A basic utility to send a byte and receive a byte. Shows the status of the send and receive flags. Up/Down to select a parameter to modify and Left/Right to change the value. Button 1 to send the selected byte. Button 2 to read a byte if one is waiting to be received. https://github.com/pmckeon/G2GTest G2GTerminal World's simplest messaging application for the Game Gear. Enter a message up to 60 characters using the directional pad and Button 1, Press Button 2 to send a message. Incoming messages display in the top window. https://github.com/pmckeon/G2GTerminal G2GTest.PNG (9.52 KB) G2GTerminal.PNG (13.31 KB) G2GTest.zip (2.05 KB) G2GTerminal.zip (2.57 KB)

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Sat Jun 26, 2021 3:32 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	Do we know which of the pins on the Gear2Gear cable hold what kind of data when the port is in "Regular" mode?

thatawesomeguy Joined: 25 Jul 2007 Posts: 731 Location: Melbourne, Australia	Posted: Sat Jun 26, 2021 8:43 pm
	PC4 (Pin 6) is serial output and PC5 (Pin 9) is serial input. The other pins are not used in this mode but can still be driven manually as inputs or outputs.

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Sun Jun 27, 2021 6:00 am
lidnariq Joined: 24 Mar 2021 Posts: 120	Do we know what bitrate?

thatawesomeguy Joined: 25 Jul 2007 Posts: 731 Location: Melbourne, Australia	Posted: Sun Jun 27, 2021 6:41 am
	Everything is documented in the official hardware reference manual https://segaretro.org/images/1/16/Sega_Game_Gear_Hardware_Reference_Manual.pdf bitrate is dependant on Baud setting which is selectable between 300, 1200, 2400, 4800 (default).

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Sun Jun 27, 2021 4:15 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	Ah! Thank you! I assumed I'd be able to find that somewhere on the SMSpower wiki but didn't think to look elsewhere afterwards (oops)

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