
FALC
56
PEF 2256 H/E
Functional Description E1/T1/J1
User’s Manual
Hardware Description
51
DS1.1, 2003-10-23
3.3
Functional Blocks
3.3.1
The communication between the CPU and the FALC
56 is done using a set of directly
accessible registers. The interface can be configured as Intel or Motorola type with a
selectable data bus width of 8 or 16 bits.
The CPU transfers HDLC data to and from the FALC
56 (through 64-byte deep FIFOs
per direction), sets the operating modes, controls function sequences, and gets status
information by writing or reading control and status registers. All accesses can be done
as byte or word accesses if enabled. If 16-bit bus width is selected, access to
lower/upper part of the data bus is determined by address line A0 and signal BHE/BLE
as shown in
Table 6
and
Table 7
.
Table 8
shows how
the ALE (
A
ddress
L
atch
E
nable) line is used to control the bus
structure and interface type. The switching of ALE allows the FALC
56 to be directly
connected to a multiplexed address/data bus.
Microprocessor Interface
3.3.1.1
Mixed Byte/Word Access to the FIFOs
Reading from or writing to the internal FIFOs (RFIFO and XFIFO) can be done using a
8-bit (byte) or 16-bit (word) access depending on the selected bus interface mode.
Randomly mixed byte/word access to the FIFOs is allowed without any restrictions.
Table 6
BHE
0
Data Bus Access (16-Bit Intel Mode)
Register Access
FIFO word access
Register word access (even addresses)
Register byte access (odd addresses)
Register byte access (even addresses)
No transfer performed
A0
0
FALC
56 Data Pins Used
D(15:0)
0
1
1
1
0
1
D(15:8)
D(7:0)
None
Table 7
BLE
0
Data Bus Access (16-Bit Motorola Mode)
Register Access
FIFO word access
Register word access (even addresses)
Register byte access (odd addresses)
Register byte access (even addresses)
No transfer performed
A0
0
FALC
56 Data Pins Used
D(15:0)
0
1
1
1
0
1
D(7:0)
D(15:8)
None