![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT94L33IB-L_datasheet_100163/XRT94L33IB-L_131.png)
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XRT94L33
3-CHANNEL DS3/E3/STS-1 TO STS-3/STM-1 MAPPER IC DATA SHEET
Rev.1.2.0.
131
Figure 5 Behavior of the Microprocessor Interface Signals, during an “Intel-type” Programmed I/O
Write Operation
ALE_AS
A[14:0]
CS*
D[7:0]
WRB_RW
Data to be Written
Address of Target Register
RdB_DS
1.3.4
PROGRAMMED I/O ACCESS IN THE MOTOROLA MODE
If the XRT94L33 is interfaced to a “Motorola-type”
C/P (e.g., the MC680X0 family, etc.); it should be
configured to operate in the “Motorola” mode. Motorola-type Programmed I/O “Read” and “Write” operations
are described below.
1.3.4.1
THE MOTOROLA MODE READ CYCLE
Whenever a “Motorola-type”
C/P wishes to read the contents of a register or some location within the
Receive J0 or J1 Message Buffer, within the XRT94L33 it should do the following.
1. 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 XRT94L33 IC.
2. Place the address of the “target” register (or buffer location) within the XRT94L33, on the Address Bus
input pins, A[14:0].
3. At the same time, the Address Decoding circuitry (within the user’s system) should assert the CS* (Chip
Select) input pin of the XRT94L33, by toggling it “l(fā)ow”.
This action enables further communication
between the
C/P and the XRT94L33 Microprocessor Interface block.
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 XRT94L33 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 XRT94L33 has now been selected.
5. Further, the
C/P should indicate that this cycle is a “Read” cycle by setting the WRB_RW (R/W*) input
pin “high”.
6. Next the
C/P should initiate the current bus cycle by toggling the RdB_DS (Data Strobe) input pin “l(fā)ow”.
This step enables the bi-directional data bus output drivers, within the XRT94L33 UNI device. 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].
After some settling time, the data on the “bi-directional” data bus will stabilize and can be read by the
C/P.
The XRT94L33 UNI will indicate that this data can be read by asserting the Rdy_Dtck (DTACK) signal.
After the
C/P detects the Rdy_Dtck signal (from the XRT94L33 UNI) it will terminate the Read Cycle by
toggling the “RdB_DS” (Data Strobe) input pin “high”.
Figure 6 presents a timing diagram which illustrates the behavior of the Microprocessor Interface signals
during a “Motorola-type” Programmed I/O Read Operation.