参数资料
型号: MCZ33780EG
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: SPECIALTY MICROPROCESSOR CIRCUIT, PDSO16
封装: 1.27 MM PITCH, ROHS COMPLIANT, SOIC-16
文件页数: 13/37页
文件大小: 851K
代理商: MCZ33780EG
Analog Integrated Circuit Device Data
20
Freescale Semiconductor
33780
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
value to DnH and/or DnL. When the minimum inter-frame
delay has been satisfied, the DSIF pin will go low, indicating
the start of a new transfer frame.
DBUS Driver/Receiver communications involve a frame
(DSIF), a data signal (DSIS), and a data return (DSIR) signal.
These are signals internal to the IC associated with the
prData is shifted out of DSIS (MSB first) and shifted into DSIR
at the same time. As a message is received, it is stored bit-
by-bit into the next available receive FIFO location. For each
data value in the receive FIFO, there is a one-bit status flag
to indicate whether or not there was a CRC error while
receiving the data. At the end of a DBUS transfer (and after
the CRC error status is stable), the RFNEn flag is set (if it was
not already) to indicate there is data in the receive FIFO to be
read.
DATA RATE
In non-spread spectrum mode, the data rate is determined
by the system clock (CLK) and the programmable clock
divider. (The Clock Divider ratio n is defined in Table 10.)
Data Rate = fCLK / (27 * n)
In spread spectrum mode, the data rate is determined by
the system clock (CLK) and the DnOFFSETL/H register
programming. Note the programmable clock divider does not
control the data rate in Spread Spectrum mode. Refer to
Register and Bit Descriptions section for details.
The following table gives the correspondence between the
offset and the data rate for fCLK = 4.0 MHz.
For other clock frequencies, the data rate can be
computed using the following formula:
Data Rate = (fCLK / 33) * (1 + OFFSET / 512)
CRC GENERATION /CHECKING
Whenever a message is sent on the DBUS, a 0- to 8-bit
CRC value is computed and serially sent as the next n bits
after the LSB of the data. The CRC length, polynomial, and
initial seed are determined by the CRCLEN[3:0],
CRCPOLY[7:0], and CRCSEED[7:0] control register fields.
The message, including the CRC bits, is passed along to a
remote peripheral, which computes a separate CRC value as
the message data is received. If this computed CRC does not
agree with the CRC value received in the message, the
peripheral device considers the message invalid.
Messages received include a 0- to 8-bit CRC value, which
was computed in the peripheral device that is responding. As
the message is received, a separate 0- to 8-bit CRC value is
computed and is compared with the CRC value in the
received message. If these values do not agree, the message
is considered invalid and the ERn status bits in the D01STAT
register are set as the receive data is transferred into the
receive data buffer.
When no remote peripheral responds to a message, the
data pattern received will be all zeros with a CRC value of 0,
which may be detected as a CRC error depending on the
values of CRCLEN[3:0], CRCPOLY[7:0], and
CRCSEED[7:0]. On the other hand, if a remote peripheral is
attached and responds with all zeros with a CRC value of
1010, this may be detected as a non-error condition.
CRC COMPUTATION
The CRC algorithm uses a programmable initialization
value, or seed, of CRCSEED[7:0] and a programmable
polynomial of CRCPOLY[7:0]. Figure 16 is a VHDL
description of the CRC algorithm for the DBUS standard 4-bit
CRC with its initial value of 1010. A seed value is chosen so
that a zero data value will generate a CRC value of 1010. A
block diagram of the default CRC calculation is shown in
--------------------------------------------------------------------------
-- Calculates the 4-bit CRC (x^4 + 1) serially for 8 to 16 bits of data.
Table 7. Data Rate versus OFFSET (Spread Spectrum)
OFFSET
Data Rate
HEX
DEC
kHz
00
0
121.2
3F
63
136.1
7A
122
150.1
9F
159
158.9
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