STN-47

Expansion Ram Cartridge Manual Ver1.02

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Contents

■ Overview

This expansion ram cartridge is an expansion cartridge that is used by connecting it to the A-Bus slot of the Sega Saturn main unit.
It contains 8Mbit (configuration: 4Mbit x 2) DRAM. It can be expanded up to 32Mbit.

■ Usage restrictions (absolute strict adherence)

Only data can be transferred to the expansion ram cartridge, and it is prohibited to put the program code regardless of whether it is directly executed or transferred.

■ About memory map

This cartridge is assigned to 22400000h to 227FFFFFh on the memory map of Sega Saturn, but the usable area is divided into the following DRAM0 and DRAM1.

         <Table 1. Memory map>

         8Mbit 32Mbit　

22400000h ┏━━━━━━━┓──┏━━━━━━━┓

         ┃ DRAM0 ┃ ┃ DRAM0 ┃

2247FFFFh ┗━━━━━━━┛ ┃ ┃

         │ │ ┃ ┃

         │ │ ┃ ┃

         │ │ ┃ ┃

22600000h ┏━━━━━━━┓──┣━━━━━━━┫

         ┃ DRAM1 ┃ ┃ DRAM1 ┃

2267FFFFh ┗━━━━━━━┛ ┃ ┃

         │ │ ┃ ┃

         │ │ ┃ ┃

         │ │ ┃ ┃

227FFFFFh └───────┘──┗━━━━━━━┛

■ Initialization

Address: Write "1" in word size to 257EFFFEh (W / O).

caution	Address: Be sure to set "1" for 257EFFFEh. If you write any other data, it will not work properly.

■ About ID

The external cartridge ID address is 24FFFFFFh (R / O), which is the same as the ID address of the "power memory". For the ID, check not only "8Mbit = 5Ah" but also "32Mbit = 5Ch" so that it can be used with 32Mbit cartridges in consideration of future expandability.
→ If you check only 8Mbit, it may not work with 32Mbit cartridge.

<Table 2 Cartridge ID>

Address = 24FFFFFFh (R / O)
Cartridge capacity	Expansion ram cartridge ID
8Mbit	5Ah
32Mbit	5Ch (reservation)

■ Corresponding peripheral character code

Describe "W" in "Corresponding peripheral (start address: 50H)" in SYSTEM ID.

example:

When using Sega Saturn standard pad + expansion ram cartridge .

“JW △△△△△△△△△△△△△△” “△” = space (20H)

reference:

"PROGRAMMER'S GUIDE" Disk format standard specifications / 4. Boot system

■ About available modes

● Reading from extended ram cartridge

• Byte read, word read, long word access and burst read are available for normal access. In addition, the CPU reads 32 bits in any case of bytes, words, and long words.

• Both SH2 and SCU DMA can be used.

● Writing to the expansion ram cartridge

• Byte light, word light, and long word light can be used in normal access. However, burst lights cannot be used.

• As for DMA, SH2 DMA can be used. SCU DMA cannot be used.

● About access speed

• It takes about 4 times as long as WORKRAM-L.

■ About A-Bus setting register and A-Bus refresh register

Regarding the A-Bus setting register, the setting is the same for both CS0 space and CS1 space, the precharge insertion bit after read is set to "1", and the number of internal waits is set to "3" for both normal and burst cycles.

For the A-Bus refresh register, set the effective bit to "1" and the internal weight number to "3".

Setting is prohibited for CS2 space and spare space.
(Users are prohibited from setting because the value set in BOOT ROM is used)

<Table 3-A-Bus setting register setting table>

A-Bus setting register address →	25FE00B0h		25FE00B4h
Settings ↓	CS0 space	CS1 space	CS2 space	Spare space
Post-write precharge insertion bit	OFF (0)	OFF (0)	Setting prohibited	Setting prohibited
Post-read precharge insertion bit	ON (1)	OFF (0)
External weight valid bit	OFF (0)	ON (1)
Burst cycle weight number setting bit	0011	1111
Normal cycle weight number setting bit	0011	1111
Burst length setting bit	00	0
Bus size setting bit	0 (16bit)	0 (16bit)

● Register settings

Specifically, set the following values.

• A-Bus setting register (25FE00B0h) = 2330 1FF0h (only CS0 and CS1 spaces are set)

• A-Bus refresh register (25FE00B8h) = 0000 0013h

reference:

"HARDWARE MANUAL" SCU User's Manual ■ A-Bus setting register

■ Access procedure

Follow the procedure below from the initialization of the Zhang ram cartridge to the memory access.

1. Check the cartridge ID. ("5Ah" for 8Mbit)
   → Please consider the support for 32Mbit (ID = 5Ch). If you check only with 8Mbit (ID = 5Ah), this application will not work when a 32Mbit expansion ram cartridge is released in the future.

2. If the cartridge ID is not recognized, display a message prompting you to connect the cartridge.

   ---message---
   

   
   The expansion ram cartridge is not inserted properly.
   
   Turn off the power and reinsert the expansion ram cartridge.
   
   

3. Write "1" in word size to the initialization address 257EFFFEh (W / O).
   → Be sure to set "1" for the word size. (Strict adherence)

4. Set the A-Bus setting register and A-Bus refresh register.
   Refer to the above ( ● Register setting value )

5. Connection completed.
   Access to the extended ram cartridge is possible.
   → Refer to the above ( ■ Available modes ) to read / write data.

■ Other

● System clock switching

When the system clock is changed using the SYS_CHGSYSCK () function The contents in the "extended ram cartridge" are not guaranteed. If you change the clock, initialize the cartridge and retransfer the data. ..

● Precautions when using the programming BOX

If SIMM is installed in the programming BOX, the address will be duplicated with the "extended ram cartridge", so disconnect the SIMM by the following method.
How to disconnect SIMM: Write 0 (zero) in the word to address 257FFFFCh.

caution	Use this program in the debugger and do not include it in the commercial version.

supplement:

If you turn off DIPSW2 "SIMMCART" in the programming BOX, you will not be able to read the ID.