■ 3.4 Peripheral access protocol

This section shows the peripheral access protocol in SH-2 direct mode.

● About peripheral port bit names

The SMPC peripheral port configuration inherits the Megadrive peripheral port to maintain compatibility with the Megadrive. Therefore, the port bit name is also handled by inheriting the name used in Mega Drive. Table 3.22 shows the correspondence between port bit numbers and port bit names. From now on, in this manual, we will proceed with the explanation using the port bit name.

Table 3.22 Correspondence between port bit numbers and port bit names

Port bit number	bit6	bit5	bit4	bit3	bit2	bit1	bit0
Port bit name	TH	TR	TL	R	L	D	U

● How to calculate Mega Dry Peripheral ID in SH-2 direct mode

The formula for calculating the Mega Drive Peripheral ID is shown below.

The Mega Dry Peripheral ID is represented by 4 bits, ID3 ID2 ID1 ID0.

ID3 ＝ R # L (TH ＝ 1)
ID2 ＝ D # U (TH ＝ 1)
ID1 ＝ R # L (TH ＝ 0)
ID0 ＝ D # U (TH ＝ 0)


# Indicates the OR.

● Port setting when acquiring Mega Drive Peripheral ID

Table 3.23 shows the port direction register settings when acquiring the MegaDrive peripheral ID. You can set the port direction as follows, read the RLDU when TH = 1 and the RLDU when TH = 0, and calculate the MegaDrive peripheral ID using the above formula.
After changing TH, lead R, L, D, and U after 2 μS.

Table 3.23 Port direction register setting values when acquiring the MegaDrive peripheral ID

Port bit name	TH	TR	TL	R	L	D	U
Port direction	Set to output	Set to input

● Mega Drive Peripheral ID for each peripheral

Table 3.24 shows the megadrive peripheral ID for each peripheral.

Table 3.24 Megadrive Peripheral ID for each peripheral

Peripheral name	Mega Drive Peripheral ID
Mega Drive 3 Button PAD	DH
Mega Drive 6 Button PAD	DH & CH
Sega Mouse	3H
Sega tap	7H
Saturn standard putt	BH
Saturn analog joystick	5H
Saturn keyboard	5H
Saturn multitap	5H

Note "Saturn standard pad", "Saturn analog joystick", "Saturn keyboard", and "Saturn multi-tap" are development names.