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PRELIMINARY
XRT86VL38
REV. P1.0.6
OCTAL T1/E1/J1 FRAMER/LIU COMBO
54
3.1.1
The Intel-Asynchronous Read-Cycle
If the Microprocessor Interface has been configured to operate in the Intel-Asynchronous Mode, then the
Microprocessor should do all of the following to perform a read operation:
1.
Place the address of the "target" register or buffer location on the Address Bus input pins A[14:0].
2.
While the microprocessor is placing this address value on the Address Bus, the Address Decoding circuitry
(within the user's system) should assert the CS* (Chip Select) pin of the XRT86VL38 device, by toggling it
"low". This action enables further communication between the microprocessor and the XRT86VL38 Micro-
processor Interface block.
3.
Toggle the ALE/AS* (Address Latch Enable) input pin "high". This step enables the "Address Bus" input
drivers, within the Microprocessor Interface block of the XRT86VL38 device.
4.
After allowing the data on the Address Bus pins to settle (by waiting the appropriate "Address" Data Setup
time"), the microprocessor should toggle the ALE/AS* pin "low". This step causes the XRT86VL38 device
to "latch" the contents of the "Address Bus" into its internal circuitry. At this point, the address of the regis-
ter or buffer locations has now been selected.
5.
Next, the microprocessor should indicate that this current bus cycle is a "Read" Operation by toggling the
RD*/DS* (Read Strobe) input pin "low". This action also enables the bi-directional data bus output drivers
of the XRT86VL38 device. At this point, the "bi-directional" data bus output drivers will proceed to drive the
contents of the "latched addressed" register onto the bi-directional data bus, D[7:0].
6.
Immediately after the microprocessor toggles the "Read Strobe" (RD*/DS*) signal "low", the XRT86VL38
device will continue to drive the RDY*/DTACK* output pin "high". The XRT86VL38 device does this in
order to inform the microprocessor that the data (to be read from the data bus) is "NOT READY" to be
"latched" into the microprocessor. In this case, the microprocessor should continue to hold the "Read
Strobe" (RD*/DS*) signal "low" until it detects the "RDY*/DTACK* output pin toggling low.
7.
After some settling time, the data on the "bi-directional" data bus will stabilize and can be read by the
microprocessor. At this time, the XRT86VL38 device will indicate that this data can be read by toggling the
RDY*/DTACK* (READY) signal "low".
8.
After the microprocessor detects the RDY*/DTACK* signal (from the XRT86VL38 device) toggling "low", it
can then terminate the Read Cycle by toggling the RD*/DS* (Read Strobe) input pin "high".
Figure 3 presents a timing diagram that illustrates the behavior of the Microprocessor Interface signals, during
an "Intel-Asynchronous" Mode Read Operation.