CHAPTER 2 PIN FUNCTIONS
63
2.2.1 System Bus Interface Signals
These signals are used when the V
R
4102 is connected to a DRAM, ROM, or LCD, or other devices in the system
through the system bus.
Table 2-1. System Bus Interface Signals (1/2)
Signal
I/O
Description of function
ADD[25..0]
O
This is a 26-bit address bus. The V
R
4102 uses this to specify addresses for the DRAM, ROM, LCD, or
system bus (ISA).
DATA[15..0]
I/O
This is a 16-bit data bus. The V
R
4102 uses this to transmit and receive data with a DRAM, ROM, LCD,
or system bus.
DATA[31..16]/
GPIO[31..16]
I/O
This function differs depending on how the DBUS32 pin is set.
<When DBUS32 = 1> : DATA[31..16]
It is the high-order 16 bits of the 32-bit data bus.
This bus is used for transmitting and receiving data between the V
R
4102 and the DRAM and ROM.
<When DBUS32 = 0> : GPIO[31..16]
It is a general-purpose I/O (GPIO) port.
LCDCS#
O
This is the LCD chip select signal. This signal is active when the V
R
4102 is performing LCD access
using the ADD/DATA bus.
RD#
O
This is active when the V
R
4102 is reading data from the LCD, RAM, or ROM.
WR#
O
This is active when the V
R
4102 is writing data to the LCD, RAM, or ROM.
LCDRDY
I
This is the LCD ready signal. Set this signal as active when the LCD controller is ready to receive
access from the V
R
4102.
ROMCS[3..0]#
O
This is the ROM chip select signal. It is used to select a ROM to be accessed from among up to four
connected ROM units.
UUCAS#/
MRAS[3]#
O
This function differs depending on how the DBUS32 pin is set.
<When DBUS32 = 1> : UUCAS#
This signal is active when a valid column address is output via the ADD bus during access of
DATA[31:24] in the 32-bit data bus.
<When DBUS32 = 0> : MRAS[3]#
This is the DRAM’s RAS signal. Up to four DRAM units can be connected, and this signal is active
when a valid row address is output via the ADD bus for the DRAM connected to the high-order
address.
ULCAS#/
MRAS[2]#
O
This function differs depending on how the DBUS32 pin is set.
<When DBUS32 = 1> ULCAS#
This signal is active when a valid column address is output via the ADD bus during access of
DATA[23:16] in the 32-bit data bus.
<When DBUS32 = 0> MRAS[2]#
This is the DRAM’s RAS signal. This signal is active when a valid row address is output via the ADD
bus for the DRAM connected to the next-highest address after the highest high-order address.
MRAS[1..0]#
O
This is the DRAM’s RAS signal.
UCAS#
O
This is the DRAM’s CAS signal. This signal is active when a valid column address is output via the
ADD bus during access of DATA[15:8] in the DRAM.
LCAS#
O
This is the DRAM’s CAS signal. This signal is active when a valid column address is output via the
ADD bus during access of DATA[7:0] in the DRAM.