GABE

GABE -- The System Control, I/O, and Sound Chip

"GABE" is the name of the system controller chip of the C256 Foenix RevC board, and performs several functions including system bus management, math coprocessing, I/O, and sound. The RevB version of the C256 had two chips "Gavin" and "Beatrix" that were combined into a single master chip called "GABE".

GABE Control Registers

Start Address	Ending Address	Register Description	Additional Info
$AF:E880		GABE_MSTR_CTRL
$AF:E881		Reserved
$AF:E882		GABE_RST_AUTH0	Must Contain the BYTE $AD for Reset to Activate
$AF:E883		GABE_RST_AUTH1	Must Contain the BYTE $DE for Reset to Activate
$AF:E884	$AF:E885	GABE_RNG_DATASEED	On read: 16-bit random data. On write, set 16-bit RNG seed.
$AF:E886		GABE_RNG_STATCTRL	On read: 8-bit status. On write: 8-bit control
$AF:E887		GABE_SYS_STAT	8-bit system status

GABE Master Control Register ($AF:E880)

7	6	5	4	3	2	1	0
GABE_CTRL_WRM_RST			GABE_CTRL_BUZZER			GABE_CTRL_SDC_LED	GABE_CTRL_PWR_LED

GABE_CTRL_PWR_LED

Turns the power LED (next to the reset button) on or off.

GABE_CTRL_SDC_LED

Turns the SDC activity LED (next to the SDC slot) on or off.

GABE_CTRL_BUZZER

Turns the built-in piezo buzzer on or off.

GABE_CTRL_WRM_RST

Triggers a warm reset of the board (GABE_RST_AUTH0 must be set to $AD and GABE_RST_AUTH1 to $DE in order to trigger the reset).

GABE System Status Register ($AF:E887)

7	6	5	4	3	2	1	0
GABE_SYS_STAT_CPUX	GABE_SYS_STAT_CPUA			GABE_SYS_STAT_EXP		GABE_SYS_STAT_MID1	GABE_SYS_STAT_MID0

GABE_SYS_STAT_CPUX

Indicates if the CPU's index registers are 8-bits or 16-bits wide.

GABE_SYS_STAT_CPUA

Indicates if the CPU's accumulator is 8-bits or 16-bits wide.

GABE_SYS_STAT_EXP

Indicates if the and expansion card is present (0).

GABE_SYS_STAT_MID1 and GABE_SYS_STAT_MID0

These two bits show the machine ID:

GABE_SYS_STAT_MID1	GABE_SYS_STAT_MID0	Machine
0	0	FMX - Development Platform
0	1	C256 Foenix - Dev Platform
1	0	C256 Foenix - User Version (65C816)
1	1	Reserved