13 Communication Functions

AGB provides the following five functions.

1. 8-Bit/32-Bit Normal Communication Function

Use of a DMG/MGB cable is prohibited for Normal Communications. It is possible to communicate with peripherals that do not use cables at 256 KHz and 2 MHz.

In extraordinary circumstances, normal communications using a communication cable exclusively for AGB is possible. However, this communication can only be performed in one direction, because of distribution and connections for multi-play communications. Also, this type of communication is only possible at 256KHz.

Communication between AGB and CGB is not possible due to differences in voltages.

2. 16-Bit Multi-player Communication Function

This multiple/simultaneous communication function uses a UART system to enable communication of up to 4 AGB units. A special cable for Multi-player communication is necessary.

3. UART Communication Function

Enables high-speed communication by UART system.

4. General Purpose Communication Function

Enables communication by any protocol through direct control of the communication terminal.

5. JOY Bus Communication Function

Enables communication using Nintendo’s standardized Joy bus.

Communication Functions 

SCCNT_L 

d15 

d14 

d13 

d12 

General Purpose 

JOY Bus 

8-Bit Serial 

32-Bit Serial 

16-Bit Serial 

UART 

13.1 8-Bit/32-Bit Normal Serial Communication

      The above figure illustrates 8 bit communication.  In 32 bit communication, the shift clock sends and receives 32 bits of  

      data.

13.2 16-Bit Multi-player Communication

Setting 

Baud Rate 

00 

9600 bps 

01 

38400 bps 

10 

57600 bps 

11 

115200 bps 

13.3 UART Communication Functions

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ERROR NAME

CONDITION

Framing Error  The receive data stop bit is not 0 
Parity Error  When parity is enabled, there is an error in the parity for the receive data  
Overrun Error  When FIFO is invalid, if the receive data is not empty (SCCNT_L[d05]=0 and next receive has ended (detect stop bit).  Or when FIFO is valid, if receive FIFO is full and next communication has ended (detect stop bit).

Setting 

Baud Rate 

00 

9600 bps 

01 

38400 bps 

10 

57600 bps 

11 

115200 bps 

13.4 General Purpose Communication

13.5 JOY Bus Communication

Direction 

Order 

d7 

d6 

d5 

d4 

d3 

d2 

d1 

d0 

Remarks 

Receive 

Command 255(FFh) 

Send 

Type Number

0400h 

Lower 8 bits of Register JSTAT 

Communication Status 

Direction 

Order 

d7 

d6 

d5 

d4 

d3 

d2 

d1 

d0 

Remarks 

Receive 

Command 0(00h) 

Send 

Type Number

0400h 

Lower 8 bits of Register JSTAT 

Communication Status 

Direction 

Order 

d7 

d6 

d5 

d4 

d3 

d2 

d1 

d0 

Remarks 

Receive 

Command 21(15h) 

Receive 

Lower 8 bits of receive data Register JOYRE_L 

Receive Data 

Upper 8 bits of receive data Register JOYRE_L 

Lower 8 bits of receive data Register JOYRE_H 

Upper 8 bits of receive data Register JOYRE_H 

Send 

Lower 8 bits of Register JSTAT 

Communication Status 

Direction 

Order 

d7 

d6 

d5 

d4 

d3 

d2 

d1 

d0 

Remarks 

Receive 

Command 20(14h) 

Send 

Lower 8 bits of send data Register JOYTR_L 

Send Data 

Upper 8 bits of send data Register JOYTR_L 

Lower 8 bits of send data Register JOYTR_H 

Upper 8 bits of send data Register JOYTR_H 

Lower 8 bits of Register JSTAT 

Communication Status 

13.6 Communication Cable