XRT7250 Datasheet, PDF (22/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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PIN DESCRIPTIONS
PIN DESCRIPTION
PIN #
1
2
3
4
5
6
NAME
NC
NC
VDD
NC
GND
Rdy_Dtck
7
WR_RW
8
CS
9
ALE_AS
DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
TYPE
DESCRIPTION
Not Bonded Out
Not Bonded Out
**** Power Supply Pin
Not Bonded Out
**** Ground Pin
O READY or DTACK
This active-low output pin will function as the READY output, when the micro-
processor interface is running in the "Intel" Mode; and will function as the
DTACK output, when the microprocessor interface is running in the "Motorola"
Mode.
"Intel" Mode - READY Output
When the Framer negates this output pin (e.g., toggles it "low"), it indicates (to
the µP) that the current READ or WRITE cycle is to be extended until this sig-
nal is asserted (e.g., toggled "high").
"Motorola" Mode - DTACK (Data Transfer Acknowledge) Output
The Framer device will assert this pin in order to inform the local microproces-
sor that the present READ or WRITE cycle is nearly complete. If the Framer
device requires that the current READ or WRITE cycle be extended, then the
Framer will delay its assertion of this signal. The 68000 family of µPs requires
this signal from its peripheral devices, in order to quickly and properly complete
a READ or WRITE cycle.
I Write Data Strobe (Intel Mode)
If the microprocessor interface is operating in the Intel Mode, then this active-
low input pin functions as the WR (Write Strobe) input signal from the µP. Once
this active-low signal is asserted, then the Framer will latch the contents of the
µP Data Bus, into the addressed register (or RAM location) within the Framer
IC. In the Intel Mode, data gets latched on the rising edge of WR
R/W Input Pin (Motorola Mode)
When the Microprocessor Interface Section is operating in the Motorola Mode,
then this pin is functionally equivalent to the R/W pin. In the Motorola Mode, a
READ operation occurs if this pin is at a logic "1". Similarly, a WRITE operation
occurs if this pin is at a logic "0".
I Chip Select Input
This active-low input signal selects the Microprocessor Interface Section of the
Framer device and enables READ/WRITE operations between the Local
Microprocessor and the Framer on-chip registers and RAM locations.
I Address Latch Enable/Address Strobe
This input is used to latch the address (present at the Microprocessor Interface
Address Bus, A[8:0]) into the Framer Microprocessor Interface circuitry and to
indicate the start of a READ/WRITE cycle. This input is active-high in the Intel
Mode (MOTO = "low") and active-low in the Motorola Mode (MOTO = "high").
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