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Signal Descriptions
External Memory Interface Pins
SYM53C825A/825AE Data Manual
4-11
Table 4-9: E xternal Memory Interface Pins
Symbol
Pin No.
Type
Description
MAS0/
137
O
Memory Address Strobe 0. T his pin is used to latch in the least sig-
nificant address byte of an external EPROM or flash memory.
Since the SYM53C825A moves addresses eight bits at a time, this
pin connects to the clock of an external bank of flip-flops which are
used to assemble up to a 20-bit address for the external memory.
Memory Address Strobe 1. T his pin is used to latch in the address
byte corresponding to address bits 15-8 of an external EPROM or
flash memory. Since the SYM53C825A moves addresses eight bits
at a time, this pin connects to the clock of an external bank of flip-
flops which assemble up to a 20-bit address for the external mem-
ory.
Memory Address/Data Bus. T his bus is used in conjunction with
the memory address strobe pins and external address latches to
assemble up to a 20-bit address for an external EPROM or flash
memory. T his bus will put out the most significant byte first and
finish with the least significant bits. It is also used to write data to a
flash memory or read data into the chip from external EPROM/
flash memory.
See MAD Bus Programming for more details.
Memory Write Enable. T his pin is used as a write enable signal to
an external flash memory.
Memory Output Enable. T his pin is used as an output enable sig-
nal to an external EPROM or flash memory during read opera-
tions.
Memory Chip Enable. T his pin is used as a chip enable signal to an
external EPROM or flash memory device
General Purpose I/O pin. Optionally, this pin is used as a Memory
Address Strobe 2 if an external memory with more than 16 bits of
addressing is specified by the pull-down resistors at power up and
bit 0 in the expansion ROM Base Address register is set.
MAS1/
136
O
MAD7-0
59, 60, 61, 62, 64,
65, 66, 67
I/O
MWE/
139
O
MOE/
140
O
MCE/
141
O
GPIO2_
MAS2/
68
I/O
Table 4-10: JTAG Pins (53C825AJ 53C825AJE Only)
Symbol
Pin No.
Type
Description
T CK
T MS
T DI
T DO
130130/
5757/
142/142
5858/
Test Clock pin for JTAG boundary scan.
Test Mode Select pin for JTAG boundary scan.
Test Data In pin for JTAG boundary scan.
Test Data Out pin for JTAG boundary scan.