Rabbit 6000 User’s Manual
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By default the I/O strobes are configured as read-only chip selects with 15 wait states and normal timing.
These settings will affect the /IORD, /IOWR, and /BUFEN signals for external I/O writes even if no other
strobe outputs are enabled in the parallel port registers.
The most common configuration of the I/O strobes is to use them a chip select signals for external devices
that share /IORD and /IOWR for the read and write strobes.
31.1.3 I/O Handshake
An external I/O handshake input can be enabled on one of the Parallel Port E pins for any combination of
the I/O banks. The external device holds this signal (active high or low) when it is busy and cannot accept
a transaction. The Rabbit 6000 will then hold midway through the transaction until either the handshake
signal goes inactive or a timeout occurs. The timeout can be defined anywhere from 32 to 2048 clocks.
When the timeout occurs, the transaction ends and a status bit is set. This bit must be checked by the pro-
gram attempting the write; no interrupt is generated.
The I/O handshake signal is sampled at the end of the first wait state (Tw). When the handshake signal is
disabled, the transition will start at the beginning of the Tw phase and continue to completion.
Figure 31.2 External I/O Handshake Timing Diagram
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