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PRELIMINARY
XRT79L71
36
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Configure the Microprocessor Interface to operate in the Intel-Asynchronous Mode by tying the PTYPE2 and
PTYPE1 pins/balls (e.g., Ball Numbers J14 and J15, respectively) to GND, and by tying PTYPE 0 (Ball Number
J16) to a logic "high".
Finally, if the Microprocessor Interface has been configured to operate in the Motorola-Asynchronous Mode,
then it will perform READ and WRITE operations as described below.
2.2.1
The Motorola-Asynchronous Read-Cycle
If the Microprocessor Interface (of the XRT79L71) has been configured to operate in the Motorola-
Asynchronous Mode, then the Microprocessor should do all of the following, anytime it wishes to read out the
contents of a register or some location within the Receive LAPD Message buffer, the Receive Cell Extraction
Memory or the Transmit Cell Extraction Memory (within the XRT79L71), it should do the following.
1.
Place the address of the "target" register (or buffer location) within the XRT79L71, on the Address Bus
Input pins, A[14:0].
2.
While the C/P is placing the address value on the Address Bus, the Address Decoding circuitry (within
the user's system) should assert the CS (Chip Select) pin of the XRT79L71, by toggling it "low". This
action enables further communication between the C/P and the XRT79L71 Microprocessor Interface
block.
3.
Assert the ALE/AS (Address-Strobe) input pin by toggling it low. This step enables the Address Bus input
drivers, within the Microprocessor Interface Block of the XRT79L71.
4.
After allowing the data on the Address Bus pins to settle (by waiting the appropriate "Address Setup"
time), the C/P should toggle the ALE/AS input pin "high". This step causes the XRT79L71 to latch the
contents of the "Address Bus" into its internal circuitry. At this point, the address of the register or buffer
location (within the XRT79L71) has now been selected.
5.
Afterwards, the C/P should indicate that this cycle is a "Read" cycle by setting the WR/R/W (R/W) input
pin "high".
6.
Next the C/P should initiate the current bus cycle by toggling the RD/DS (Data Strobe) input pin "low".
This step enables the bi-directional data bus output drivers, within the XRT79L71. At this point, the bi-
directional data bus output drivers will proceed to driver the contents of the "Address" register onto the bi-
directional data bus, D[7:0].
7.
Immediately after the C/P toggles the "Data Strobe" (RD/DS) signal "low", the XRT79L71 will continue
to drive the RDY/DTACK output pin "high". The XRT79L71 does this in order to inform the C/P that the
data (to be read from the data bus) is "NOT READY" to be latched into the C/P. In this case, the C/P
should continue to hold the "Data Strobe" (RD/DS) signal "low" until it detects the RDY/DTACK output pin
toggling "low".
8.
After some settling time, the data on the "bi-directional" data bus will stabilize and can be read by the C/
P. The XRT79L71 will indicate that this data can be read by asserting the RDY/DTACK (DTACK) output
signal (by toggling it "low").
9.
After the C/P detects the RDY/DTACK signal (from the XRT79L71) toggling "low", it can terminate the
Read Cycle by toggling the "RD/DS" (Data Strobe) input pin "high".
Figure 8 presents a timing diagram that illustrates the behavior of the Microprocessor Interface signals during
a "Motorola-Asynchronous" Read Operation.