315-5308

The 315-5308 is found on earlier revisions of the MegaDrive I.

It is the bus arbiter that controls all bus accesses.

315-5308

Pinout

OpenOffice Draw file : File:315-5308.odg

Signals

Address Buses
A1-A23	M68K Address Bus
ZA0-ZA15	Z80 Address bus
Data Buses
D0-D15	M68K Data bus
ZD0-ZD7	Z80 Data bus
IO port lines
EM1X	Port 1 lines
EM2X	Port 2 lines
EM3X	Port 3 lines
Control lines
M68K related control lines
/BG	Bus Grant
/BGACK	Bus Grand Acknowledge
/BR	Bus Request
FC0	Function Code 0, 1 = Accessing user data
FC1	Function Code 1, 1 = Accessing user program
/HALT	Halt 68K execution
/RESET	Reset 68K
/VPA	Valid Peripheral Access
/AS	Address strobe
/DTACK	Data Acknowledge
/UDS	Accessing even bytes
/LDS	Accessing odd bytes
R/W	Read/Write pin, 0 = write 1 = read
Z80 related control lines
/ZM1	Opcode fetch strobe
/ZRD	Read strobe
/ZWR	Write strobe
/ZMREQ	Memory request
/ZIORQ	IO request
/ZNMI	Non-maskable IRQ
/ZBR	Bus request
/ZBAK	Bus Acknowledge
/ZRES	Reset Z80
/ZWAIT	Wait
Address decoding related control lines
/ASEL	Read or Write on $000000-$7FFFFF region
/CAS0	Read or Write on $000000-$DFFFFF region
/RAS0	Read or Write on $E00000-$FFFFFF region, act as /CE signal for the RAM chips
/CE0	Chip Enable for the cartridge, low when accessing $000000-$3FFFFF region when expension unit isn't inserted or $400000-$7FFFFF when it is.
/TIME	Read or Write on $A13000-$A130FF region
/LWR	Lower byte WRite
/UWR	Upper byte WRite
/NOE	/OE signal for the lower part of the RAM
/EOE	/OE signal for the upper part of the RAM
/ZREF	Unknown, tied to unused pin #1 of Z80 RAM
/ZRAM	/CE for the Z80 RAM
Configuration related control lines
/DISK	0V Expansion Unit connected
FREQ	5V = 60Hz, 0V = 50Hz
/FRES
LANG	5V = English, 0V = Japanese
/M3	Mark III compatibility mode
VRAM related control lines
/CAS1	Column address strobe
/RAS1	Row address strobe
/SE0	Serial data bus /OE
SC	Serial clock
/WE0	Write enable
/OE1	Output enable
Clock lines
MCLK	Master Clock
VCLK	68K clock
ZCLK	Z80 clock
EDCLK	Unknown clock