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R
XCR3320: 320 Macrocell SRAM CPLD
DS033 (v1.1) February 10, 2000
1-800-255-777814
Configuration Data Format
Overview
The XCR3320 functionality is determined by the state of
internal configuration RAM. This section discusses the con-
figuration data format, and the function of each field in con-
figuration data packets.
Configuration Data Packets
Configuration of the XCR3320 is done using configuration
packets. The configuration packet is shown in
Figure 11
.
The data packet consists of a header and a data frame.
There are four types of data frames. The header is shifted
into the device first, followed by one data frame. Configura-
tion of a single XCR3320 requires 338 data packets, one for
each address. All preceding data must contain only 1
’
s.
Once a device is configured, it retransmits data of any
polarity. Before and during configuration, all data retrans-
mitted out the daisy-chain port (dout) are 1
’
s.
The ordering of the data packets may be random, but they
cannot be mixed with other devices
’
data packets. Align-
ment bits are not required between data packets. If used,
alignment bits must be included in the length count, and
they must be at least 2-bits long.
The header is fixed and consists of five fields:
Leading 1s,
Preamble,
CRC Enable,
CRC Bits,
Compression Bits.
The leading 1s enter the device first. The following is a
description of each field in the header.
Leading 1s:
This is a four or greater bit field consisting of 1s.
Preamble/Postamble:
This is a four bit field which indicates the start of a
frame or the end of configuration:
Preamble: -0010 - signals the beginning of a config-
uration data packet.
Postamble: 0100 -signals the end of configuration.
All other values of the preamble field force configu-
ration of the entire system to restart.
The segments CRC Enable, CRC Bits, and Compression
Bits are valid only if the Preamble field is 0010.
Cyclic Redundancy Check (CRC) Enable:
In this single bit field, a 0 disables CRC checking of
the data stream. If the CRC is disabled the 16 bit
CRC field must be the default described below. A1
enables CRC error checking of the data stream.
CRC Error Checking:
The CRC field is a 16 bit field. The default value is
1010_1010_1010_1010. The calculated value is
from data, address, stop bit, and first alignment bit
(starting with crc_reg[15:0] = [0]). Using verilog
operators, the crc is calculated as:
crc_reg[14:2] <= cr_reg[14:2] << 1;
cr_reg[2] <= cr_reg[15]^din^cr_reg[1];
cr_reg[1] <= cr_reg[0];
cr_reg[0] < cr_reg[15]^din;
cr_reg[15] <= cr_reg[15]^din^cr_reg[14];
If a CRC error is detected, configuration is halted
and must be restarted.
Figure 11: Data Packet
Table 4: Configuration Frame Size
Device
XCR3320
338
560
14
560
560
189280
Number of frames
Data bits/standard frame
Data bits/compressed frame
Data bits/user_code frame
Data bits/isc_code frame
Maximum configuration
data
–
# bits/frame x # frames
DATA FRAME
HEADER
LSB
MSB
27
SP00593
Figure 12: 27-bit Header
COMPRESSION
BITS
CRC
BITS
CRC
ENABLE
PREAMBLE/
POSTAMBLE
LEADING 1s
2
16
1
4
4
SP00594
MSB
LSB
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