
Data Sheet
June 1999
ORCA Series 2 FPGAs
Lucent Technologies Inc.
51
FPGA Configuration Modes
 (continued)
Daisy Chain
Multiple FPGAs can be configured by using a daisy 
chain of the FPGAs. Daisy chaining uses a lead FPGA 
and one or more FPGAs configured in slave serial 
mode. The lead FPGA can be configured in any mode 
except slave parallel mode. (Daisy chaining is not avail-
able with the boundary-scan ram_w instruction, dis-
cussed later.)
All daisy-chained FPGAs are connected in series. 
Each FPGA reads and shifts the preamble and length 
count in on positive CCLK and out on negative CCLK 
edges. 
An upstream FPGA that has received the preamble 
and length count outputs a high on DOUT until it has 
received the appropriate number of data frames so that 
downstream FPGAs do not receive frame start bits 
(0s). After loading and retransmitting the preamble and 
length count to a daisy chain of slave devices, the lead 
device loads its configuration data frames. The loading 
of configuration data continues after the lead device 
has received its configuration data if its internal frame 
bit counter has not reached the length count. When the 
configuration RAM is full and the number of bits 
received is less than the length count field, the FPGA 
shifts any additional data out on DOUT. 
The configuration data is read into DIN of slave devices 
on the positive edge of CCLK, and shifted out DOUT 
on the negative edge of CCLK. Figure 46 shows the 
connections for loading multiple FPGAs in a daisy-
chain configuration. 
The generation of CCLK for the daisy-chained devices 
which are in slave serial mode differs depending on the 
configuration mode of the lead device. A master paral-
lel mode device uses its internal timing generator to 
produce an internal CCLK at eight times its memory 
address rate (RCLK). The asynchronous peripheral 
mode device outputs eight CCLKs for each write cycle. 
If the lead device is configured in either synchronous 
peripheral or a slave mode, CCLK is routed to the lead 
device and to all of the daisy-chained devices.
The development system can create a composite 
configuration bit stream for configuring daisy-chained 
FPGAs. The frame format is a preamble, a length count 
for the total bit stream, multiple concatenated data 
frames, an end-of-configuration frame per device, a 
postamble, and an additional fill bit per device in the 
serial chain.
As seen in Figure 46, the 
INIT
 pins for all of the FPGAs 
are connected together. This is required to guarantee 
that powerup and initialization will work correctly. In 
general, the DONE pins for all of the FPGAs are also 
connected together as shown to guarantee that all of 
the FPGAs enter the start-up state simultaneously. This 
may not be required, depending upon the start-up 
sequence desired.
5-4488(F)
Figure 46. Daisy-Chain Configuration Schematic
V
DD
EPROM
PROGRAM
D[7:0]
OE
CE
A[17:0]
A[17:0]
D[7:0]
DONE
M2
M1
M0
DONE
HDC
LDC
RCLK
CCLK
DIN
DOUT
DOUT
DIN
CCLK
DONE
DOUT
INIT
INIT
INIT
CCLK
V
V
DD
 OR
GND
PRGM
PRGM
M2
M1
M0
PRGM
M2
M1
M0
V
DD
V
DD
HDC
LDC
RCLK
HDC
LDC
RCLK
V
DD
ORCA
SERIES
FPGA
SLAVE #2
ORCA
SERIES
FPGA
MASTER
ORCA
SERIES
FPGA
SLAVE #1