Digital Blocks
CY8C24xxx Preliminary Data Sheet
210
Document No. 38-12011 Rev. *E
December 22, 2003
17.2.1.3
Dead Band Register Definitions
17.2.1.4
CRCPRS Register Definitions
Bank 0:
There are three 8-bit data registers and a 3-bit control register.
Table 17-8
explains the meaning of these registers in the context of Dead Band
operation.
Bank 1:
The Mode bits in the Function register are block type specific. Other bit fields in this register, as well as the definitions of the Input and Output reg-
isters, are common to all functions.
Mode [1:0] is encoded as the Kill Type. In all cases, the output is forced low immediately. Mode bits are encoded for Kill options and are detailed
in the following table.
Reference
“Dead Band Timing” on page 216
for additional information on the Dead Band Kill options.
Table 17-8. Dead Band Register Descriptions
Name
Function
Count Value
Description
DR0
Not Directly Readable or Writeable.
During normal operation, DR0 stores the current count of a synchronous down counter.
When disabled, a write to the DR1 Period register is also simultaneously loaded into DR0 from the data bus.
When disabled, a read of DR0 returns 00h to the data bus and transfers the contents of DR0 to DR2.
Write Only Register.
Data in this register sets the period of the dead band count. The actual number of clocks counted is Period + 1. The mini-
mum period value is 00h, which sets a dead band time of one clock.
When disabled, a write to this register also transfers the period value directly into DR0.
When enabled, if the block frequency is 24 MHz or below, this register may be written to at any time, but the period will only
be reloaded into DR0 in the clock following a terminal count. If the block frequency is 48 MHz, the terminal count or compare
interrupt should be used to synchronize the new Period register write; otherwise, the counter could be incorrectly loaded.
When disabled, a read of DR0 will transfer the contents of DR0 into DR2.
DR1
Period
DR2
Buffer
Bank 0:
There are three data registers and one control register.
Table 17-9
explains the meaning of these registers in the context of CRCPRS operation.
Note that in the CRCPRS function, a write to the DR2 Seed register is also loaded simultaneously into DR0.
Bank 1:
The mode bits in the Function register are block type specific. Other bit fields in this register, as well as the definitions of the Input and Output reg-
isters, are common to all functions and are described in the
“DxBxxIN Registers” on page 214
and the
“DxBxxOU Registers” on page 214
.
The mode bits are encoded to determine the Compare type.
Table 17-9. CRCPRS Register Descriptions
Name
Function
LFSR
Description
DR0
Not Directly Readable or Writeable.
During normal operation, DR0 stores the state of a synchronous Linear Feedback Shift Register.
When disabled, a write to the DR2 Seed register is also simultaneously loaded into DR0 from the data bus.
When disabled, a read of DR0 returns 00h to the data bus and transfers the contents of DR0 to DR2. This register should not
be read while the block is enabled.
Write Only Register.
Data in this register sets the polynomial for the CRC or PRS function.
Exception
: This register must only be written when the block is disabled.
Read Write Register.
DR2 functions as a Seed and Residue register.
When disabled, a write to this register also transfers the seed value directly into DR0.
When enabled, DR2 may be written to at any time. Value written will be used in the Compare function.
When enabled, the compare output is computed using the Compare Type (set in the Function register mode bits) between
DR0 and DR2. The result of the compare is output to the auxiliary output.
When disabled, a read of DR0 will transfer the contents of DR0 into DR2. This feature can be used to read out the residue,
after a CRC operation is complete.
DR1
Polynomial
DR2
Seed/Residue