Book Analog Interfacing to Embedded Microprocessors
Bus Relinquish
The MAX151 has a maximum bus relinquish time of 100 ns. This means that
the MAX151 can drive the data bus up to 100 ns after the -RD signal goes
high. If the processor tries to start another cycle immediately after reading
the MAX151 result, this may result in bus contention. A typical example would
be the 80186 processor, which multiplexes the data bus with the address bus;
at the start of a bus cycle the data bus is not tristated, but the processor drives
the address onto the data bus. If the MAX151 is still driving the bus, this can
result in an incorrect bus address being latched.
The solution to this problem is to add a data bus buffer between the
MAX151 and the processor. The buffer inputs are connected to the MAX151
data bus outputs, and the buffer outputs are connected to the processor data
bus. The buffer is turned on when -RD and -CS are both low, and turned off
when either goes high
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