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Signal Descriptions
External Memory Interface Pins
SYM53C875/875E Data Manual
4-17
Table 4-11: E xternal Memory Interface Pins
Symbol
Pin No.
53C875, 53C875J/
53C875N/53C875JB
Type
Description
MAS0/
137/179/A8
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 SYM53C875 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 SYM53C875 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.
MAS1/
136/178/B8
O
MAD7-0
53C875,
SYM53C875E,
SYM53C875J,
SYM53C875JE:
59, 60, 61, 62, 64,
65, 66, 67 59, 60,
61, 62, 64, 65, 66,
67
SYM53C875N:
78, 79, 80, 81, 83,
84, 85, 86
SYM53C875JB,
SYM53C875JBE:
L7, M7, N7, K 7,
M8, N8, L8, K 8
139/181/C7
I/O
MWE/
O
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.
MOE/
140/182/B7
O
MCE/
141/183/A7
O
GPIO2_
MAS2/
68 /87/J8
I/O