◆ Saturn Peripheral ID

● Composition of Saturn Peripheral ID

The Saturn Peripheral ID consists of the peripheral type and data size. The Saturn Peripheral ID allows you to recognize the structure and content of peripheral data. The configuration of the Saturn Peripheral ID is shown in Figure 3.15.

Figure 3.15 Saturn Peripheral ID Configuration

bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
Sega Saturn Peripheral Type				Data size

Saturn peripheral type

Saturn peripheral type indicates the type of peripheral. Therefore, it can be used to recognize how the peripheral data is arranged. Saturn currently defines four peripheral types and presents them as standard formats. See the Saturn Peripheral Standard Format section for more information.

Data size

The data size indicates how many bytes of peripheral data are output after the Saturn peripheral ID. Therefore, by using the data size, it is possible to recognize how many bytes of peripheral data table are configured.
You can also see where the head of the next peripheral's data table is.

● Details of Saturn Peripheral ID

<When the peripheral is directly connected to the peripheral port>

The Saturn Peripheral defines a data size of up to 255 bytes.
Saturn peripherals include peripherals that are 15 bytes or less and peripherals that are 16 bytes or more and 255 bytes or less. In addition, there are 15-byte mode and 255-byte mode in port mode. Therefore, there are four possible combinations of peripheral data size and port mode shown in Table 3.8, and the configuration of Saturn peripheral ID and peripheral data is as shown in Figures 3.16 to 3.18.

Table 3.8 Peripheral data size and port mode combinations

(When the peripheral is directly connected to the peripheral port)

		Port mode (IREG1 setting)
		15	255
Peripheral data size [bytes]	15	Peripheral data structure 1
	16-255	Peripheral data structure 2	Peripheral data structure 3

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Figure 3.16 Peripheral data structure 1

Saturn Peripheral ID	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	0H ~ EH Saturn peripheral type				1H ~ FH Data size

Peripheral data table	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	Peripheral data 1st
	Peripheral data 2nd
	:: :: ::
	Peripheral data nth

nth is indicated by the data size and can be up to 15.

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Figure 3.17 Peripheral data structure 2

Saturn Peripheral ID	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	0H ~ EH Saturn peripheral type				0H Data size
Extended data size	0H				F0H

Peripheral data table	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	Peripheral data 1st
	Peripheral data 2nd
	:: :: ::
	Peripheral data nth

Limit the extended data size to 15 bytes.

Peripheral development does not allow combinations where the extended data size is 0FH when accessed in 255-byte mode.

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Figure 3.18 Peripheral data structure 3

Saturn Peripheral ID	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	0H ~ EH Saturn peripheral type				0H Data size
Extended data size	10H ~ FFH

Peripheral data table	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	Peripheral data 1st
	Peripheral data 2nd
	:: :: ::
	Peripheral data nth

nth is indicated by the extended data size and has a maximum of n = 255 .

<When a multi-tap is connected to the peripheral port>

When multi-tap connected, port mode indicates the maximum data size to collect from the peripherals connected to each tap. (Not the total number of data collected from the entire multitap.)
If the connected peripheral is 15 bytes or less, the peripheral data configuration is 1 regardless of whether the port mode is 15-byte mode or 255-byte mode.
If the connected peripheral is 16 bytes or more and the port mode is 15 bytes mode, it collects only up to 15 bytes as in peripheral data configuration 2.
If the connected peripheral is 16 bytes or more and the port mode is 255 bytes mode, all data is collected as in peripheral data configuration 3.
Also, if the specifications of the multi-tap itself is a maximum of 15 bytes for each tap, data of 16 bytes or more will be cut.
Multitap can be connected with a mixture of peripherals of 15 bytes or less and peripherals of 16 bytes or more. However, when issuing the INTBACK command, the port mode can only be set to either 15 bytes or 255 bytes.
Therefore, as a multi-tap specification, the maximum data size that each tap can collect is defined. When using multi-tap, set the port mode according to the maximum data size of the tap. That is, if the multi-tap specification is up to 15 bytes, set the port mode to 15-byte mode, and if the multi-tap specification is up to 255 bytes, set the port mode to 255-byte mode.
The maximum size of Saturn 6P multi-tap is 15 bytes per tap. Use the port mode in 15-byte mode.
Table 3.9 shows the combinations of multi-tap data size and port mode. Peripheral data structures 1 to 3 in Table 3.9 are similar to those shown in Figures 3.16 to 3.18.
The connection status of each tap when using multi-tap is indicated by the Saturn peripheral ID of each tap. When not connected to the tap and when the UNKNOWN device is connected to the tap, the Saturn peripheral ID is output with the configuration shown in Figure 3.19 and Figure 3.20.

Table 3.9 Combinations of peripheral data size and port mode (multi-tap)

		Port mode (IRG1 setting)
		15	255
Peripheral data size [bytes]	15	Peripheral data structure 1
	16-255	Peripheral data structure 2	Peripheral data structure 3
	disconnected	Tap peripheral not connected
	UNKNOWN	Tap peripheral UNKNOWN

Figure 3.19 Saturn peripheral ID when no peripheral is connected to the tap

Saturn Peripheral ID	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	FFH

Figure 3.20 Saturn peripheral ID when UNKNOWN peripheral is connected to the tap

Saturn Peripheral ID	bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
	FH Saturn peripheral type				0H ~ EH Data size

Outputs the MegaDrive peripheral ID to the data size.

It can be treated in the same way as SMPC UNKNOWN.