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3.2.3 Fast RAM Configuration (U9 and U10)
Devices installed in the fast RAM sockets (U9 & U10) provide emulation for internal ROM
memory with maximum speed interfacing. While most MCU-internal ROM can be accessed with
fast termination, the signal delay created from the PAL may inhibit the usage of the pseudo ROM
sockets for ROM code emulation. Therefore, to provide the fastest access times, the fast RAM
sockets are connected directly to the MCU.
The fast RAM sockets accept: 32K x 8, or 128K x 8 fast static RAM devices that fit the standard
pin-outs as shown in Figure 3-5. The fast RAM sockets accept memory devices of three types:
300 mil or 400 mil DIP devices, or 400 mil SOJ devices. The 400 mil SOJ devices require a SOJ
to ZIP test socket. One recommended manufacturer of the SOJ to ZIP test socket is:
Wells Electronics Inc., Welcon Part # 644-2320312.
Fast RAM is enabled by a single MCU chip select. Jumper header W14 lets you select any MCU
chip select signal as the fast RAM chip select (refer to paragraph 3.2.3.1 for a description of
jumper header W14).
Fast RAM is configured as a word port. Fast RAM is directly connected to the MCU and
controlled by a single MCU chip select. Fast RAM supports all memory read cycles (byte, word,
or long word). Since fast RAM is a word port, it can only support aligned word or aligned long
word write cycles. The fast RAM sockets cannot be used as a byte port. The MCU's A0 address
signal is not connected to the memory sockets.
Byte, mis-aligned word or mis-aligned long word writes to fast
RAM devices corrupts memory contents by performing a word
write operation. Always write data with aligned word or aligned
long word operations.
When using high-level languages, such as C, an operation
modifying a single bit of a word/long word variable may generate a
byte accessing instruction, such as bit set or bit clear.
The memory configurations shown in Figure 3-4 are only three of
the possible methods for configuring memory in sockets U9 &
U10.
M68MPFB1632/D
CAUTION
NOTE
3-19
MEMORY CONFIGURATION
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