■3.4 Peripheral access protocol

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

●About peripheral port bit names

The configuration of the SMPC peripheral port is inherited from the Mega Drive peripheral port in order to maintain compatibility with the Mega Drive. Therefore, we have decided to inherit the port bit names from the Mega Drive. Table 3.22 shows the correspondence between port bit numbers and port bit names. From now on, this manual uses port bit names for explanations.

Table 3.22 Correspondence between port bit number and port bit name

port bit number	bit6	bit5	bit4	bit3	bit2	bit1	bit0
port bit name	T.H.	T.R.	T.L.	R	L	D	U

●Megadrive peripheral ID calculation method in SH-2 direct mode

The Mega Drive peripheral ID calculation formula is shown below.

Megadrive 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 logical sum (OR).

●Port settings when acquiring Mega Drive peripheral ID

Table 3.23 shows the port direction register settings when acquiring the Mega Drive peripheral ID. You can set the port direction as shown below, read the RLDU when TH=1 and the RLDU when TH=0, and calculate the Mega Drive peripheral ID using the above formula.
Please read R, L, D, and U after 2μs after TH changes.

Table 3.23 Port direction register setting value when acquiring Mega Drive peripheral ID

port bit name	T.H.	T.R.	T.L.	R	L	D	U
port direction	set to output	set to input

●Megadrive peripheral ID of 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
Megadrive 3 button PAD	DH
Megadrive 6 button PAD	DH&CH
sega mouse	3H
sega tap	7H
saturn standard pad	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.