XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
á
PRELIMINARY
REV. P1.1.3
51
A.1
Assert the ALE_AS (Address Strobe) input pin
by toggling it "Low". This step enables the
Address Bus input drivers (within the
XRT72L50 DS3/E3 Framer).
A.2
Place the address of the initial target register or
buffer location (within the Framer), on the
Address Bus input pins, A[10:0].
A.3
At the same time, the Address-Decoding cir-
cuitry (within the user's system) should assert
the CS input pin of the Framer by toggling it
"Low". This step enables further communica-
tion between the μC/μP and the Framer Micro-
processor Interface block.
A.4
After allowing the data on the Address Bus pins
to settle (by waiting the appropriate Address
Setup time), the μC/μP should toggle the
ALE_AS input pin "High". This step causes the
Framer device to latch the contents of the
Address Bus into its own circuitry. At this point,
the initial address of the burst access has now
been selected.
A.5
Further, the μC/μP should indicate that this cur-
rent bus cycle is a Write operation by toggling
the
WR_R/W
(R/W) input pin "Low".
A.6
The μC/μP should then place the byte or word
that it intends to write into the target register, on
the bi-directional data bus, D[7:0].
A.7
Next, the μC/μP should initiate the bus cycle by
toggling the RD_DS (Data Strobe) input pin
"Low". When the XRT72L50 DS3/E3 Framer
device senses that the
WR_R/W
input pin is
"Low", and that the RD_DS input pin has tog-
gled "Low" it will enable the input drivers of the
bi-directional data bus, D[7:0].
A.8
After waiting the appropriate amount of time, for
this newly placed data to settle on the bi-direc-
tional data bus (e.g., the Data Setup time) the
Framer will assert the RDY_DTCK (DTACK)
output signal.
A.9
After the μP/μC detects the RDY_DTCK signal
(from the Framer) it should toggle the RD_DS
input pin "High". This action accomplishes two
things:
a.
It latches the contents of the bi-directional data
bus into the XRT72L50 DS3/E3 Framer Micropro-
cessor Interface block.
b.
It terminates the Write cycle.
Figure 35 presents a timing diagram which illustrates
the behavior of the Microprocessor Interface signals,
during the Initial write operation within a Burst Ac-
cess, for a Motorola-type μC/μP
At the completion of this initial write cycle, the μC/μP
has written a byte or word into the first register or
buffer location (within the XRT72L50 DS3/E3 Framer)
for this particular burst I/O access. In order to illus-
trate how this burst I/O cycle works, the byte (or word)
of data, that is being written in Figure 35 has been la-
beled Data to be Written (Offset = 0x00).
2.2.2.2.2.2.2
The Subsequent Write Operations
F
IGURE
35. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
SIGNALS
,
DURING
THE
I
NITIAL
W
RITE
O
PERATION
OF
A
B
URST
C
YCLE
(M
OTOROLA
-
TYPE
P
ROCESSOR
)
RDY_DTCK
ALE_AS
A(8:0)
CS
D(7:0)
RD_DS
WR_R/W
Data to be Written
(Offset = 0x00)
Address of "Initial" Target Register (Offset = 0x00)