HD64570 Datasheet, PDF (126/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

Bit 3: Reserved. This bit always reads 0 and must be set to 0.
Bit 2 (CRCCC: CRC Code Calculation): Specifies CRC code generation/detection in byte
synchronous or bit synchronous mode.
• Asynchronous mode
Reserved. This bit always reads 0 and must be set to 0.
• Byte synchronous/Bit synchronous mode
CRCCC = 0: Disables CRC code generation/detection.
CRCCC = 1: Enables CRC calculation for transmission and reception in byte or bit
synchronous mode. Results of the CRC calculation for transmission are sent as CRC codes,
while results of the CRC calculation for reception are reflected by the CRCE bit of status
register 2 (ST2).
Deletes FCS (CRC) without transferring it to the receive buffer in bit synchronous mode.
The polarity of the CRC code on the transmit and receive data lines depends on the protocol mode
as follows:
Byte synchronous: The calculated CRC value is transmitted on the TXDM line without
complementation, regardless of the setting of bits CRC1 and CRC0.
In received CRC calculations, the CRC value on the RXCM line is regarded as non-
complemented.
Bit synchronous: The one's complement of the calculated CRC value is transmitted on the TXDM
line, regardless of the setting of bits CRC1 and CRC0. In received CRC calculations, the CRC
value on the RXDM line is regarded as a one's complement.
Bits 1−0 (STOP1−STOP0/CRC1−CRC0: Stop Bit Length/CRC Calculation Expression and
Initial Value): Specify the stop bit length in asynchronous mode and the CRC calculation
expression in bit or byte synchronous mode.
• Asynchronous mode
STOP1, STOP0 = 0, 0: Stop bit length = 1
STOP1, STOP0 = 0, 1: Stop bit length = 1.5
STOP1, STOP0 = 1, 0: Stop bit length = 2
STOP1, STOP0 = 1, 1: Reserved
• Byte synchronous/Bit synchronous mode
CRC1 = 0: Specifies CRC-16 (X16 + X15 + X2 + 1) for CRC calculators in the transmitter
and receiver
CRC1 = 1: Specifies CRC-CCITT (X16 + X12 + X5 + 1) for CRC calculators in the
transmitter and receiver
CRC0 = 0: Specifies all 0s as the CRC calculator initial value
Rev. 0, 07/98, page 110 of 453