
á
á THREE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER XRT72L53
PRELIMINARY
REV. P1.1.7
56
the C/P should toggle the WR_R/W (Write
Strobe) input pin "High". This action accom-
plishes two things:
a. It latches the contents of the bi-directional data
bus into the XRT72L53 DS3/E3 Framer Micropro-
cessor Interface block.
b. It terminates the write cycle.
Figure 26 presents a timing diagram which illustrates
the behavior of the Microprocessor Interface signals,
during an Intel-type Programmed I/O Write Opera-
tion.
2.3.2.1.2
Programmed I/O Access in the Motor-
ola Mode
If the XRT72L53 DS3/E3 Framer is interfaced to a
Motorola-type C/P (e.g., the MC680X0 family, etc.),
it should be configured to operate in the Motorola
mode (by tying the MOTO pin to Vcc). Motorola-type
Programmed I/O Read and Write operations are de-
scribed below.
2.3.2.1.2.1
The Motorola Mode Read Cycle
Whenever a Motorola-type C/P wishes to read the
contents of a register or some location within the Re-
ceive LAPD Message or Receive OAM Cell Buffer,
(within the Framer) 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 Framer IC.
2. Place the address of the target register (or buffer
location) within the Framer, on the Address Bus
input pins, A[10:0].
3. At the same time, the Address Decoding circuitry
(within the user's system) should assert the CS
(Chip Select) input pin of the Framer, by toggling
it "Low". This action enables further communica-
tion between the C/P and the Framer Micropro-
cessor 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
Framer 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
Framer) has now been selected.
5. Further, 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 XRT72L53
DS3/E3 Framer. At this point, the bi-directional
data bus output drivers will proceed to driver the
contents of the Address register onto the bi-direc-
tional data bus, D[7:0].
7. After some settling time, the data on the bi-direc-
tional data bus will stabilize and can be read by
the C/P. The XRT72L53 DS3/E3 Framer will
indicate that this data can be read by asserting
the RDY_DTCK (DTACK) signal.
8. After the C/P detects the RDY_DTCK signal
(from the XRT72L53 DS3/E3 Framer) it will termi-
FIGURE 26. BEHAVIOR OF THE MICROPROCESSOR INTERFACE SIGNALS, DURING AN INTEL-TYPE PROGRAMMED I/O
WRITE OPERATION
ALE_AS
A(10:0)
CS
D(7:0)
RD_DS
WR_R/W
RDY_DTCK
Data to be Written
Address of Target Register