AD1816A

–29–

REV. A

[Base+14]

Joystick Position Data Low Byte

76543210

JAXIS [7:0]

RESET = [0xFF]

JAXIS [7:0]

(RO)

Joystick Axis Low Byte.

Note: Axis to be read through this register is selected by the JSEL bits in the control register. A write to this register starts a sampling

cycle.

[Base+15]

Joystick Position Data High Byte

76543210

JAXIS [15:8]

RESET = [0xFF]

JAXIS [15:8]

(RO)

Joystick Axis High Byte.

Note: Axis to be read through this register is selected by the JSEL bits in the control register. A write to this register starts a sampling

cycle

Sound System Indirect Registers

Writing Indirect Registers

All Indirect Registers must be written in pairs: low byte followed by high byte. The Indirect Address Register [SSBASE+0] holds the

address for a register pair, the Indirect Low Data Byte [SSBASE+2] is used to write low data byte and the Indirect High Data Byte

[SSBASE+3] is used to write the high data byte. The low data byte is held in the temporary register until the upper byte is written.

Programming Example

“Write Sample Rate for Voice Playback at 11,000 Hz (0x2AF8)”

1) Write [SSBASE+0] with 0x02

; indirect register for voice playback sample rate

2) Write [SSBASE+2] with 0xF8

; low byte of 16-bit sample rate register

3) Write [SSBASE+3] with 0x2A

; high byte of 16-bit sample rate register

Reading Indirect Registers

All indirect registers can be individually read. The Sound System Indirect Address Register [SSBASE+0] holds the address for a reg-

ister pair, the Indirect Low Data Byte [SSBASE+2] is used to read low data byte and Indirect High Data Byte [SSBASE+3] is used

to read the High data byte.

Programming Example

“Read Sample Rate for Voice Playback set to 11,000 Hz (0x2AF8)”

1) Write [SSBASE+0] with 0x02

; indirect register for voice playback sample rate

2) Read [SSBASE+2]

; low byte of 16-bit sample rate register set to 0xF8

3) Read [SSBASE+3]

; high byte of 16-bit sample rate register set to 0x2A

ISR Saves and Restores

For Interrupt Service Routines, ISRs, it is necessary to save and restore the Indirect Address and the Low Byte Temporary Data

holding registers inside the ISR.

Programming Example

“Save/Restore during an ISR”

Beginning of ISR:

1) Read [SSBASE+0]

; save Indirect Address register to TMP_IA

2) Write [SSBASE+0] with 0x00;

; indirect Register for Low Byte Temporary Data

3) Read [SSBASE+2]

; save Low Byte Temporary data to TMP_LBT

4) ISR Code

; ISR routine

5) Write [SSBASE+2] with TMP_LBT

; restore Low Byte Temporary data TMP_LBT

6) Write [SSBASE+0] with TMP_IA

; restore Indirect Address Register to TMP_IA

7) Return from Interrupt

; return from ISR