DU(4) Kernel Interfaces Manual DU(4)
du, dp - DU-11 201 data-phone interface
The dp0 file is a 201 data-phone interface. Read and write calls to
dp0 are limited to a maximum of 512 bytes. Each write call is sent as
a single record. Seven bits from each byte are written along with an
eighth odd parity bit. The sync must be user supplied. Each read call
returns characters received from a single record. Seven bits are
returned unaltered; the eighth bit is set if the byte was not received
in odd parity. A 10 second time out is set and a zero-byte record is
returned if nothing is received in that time.
The name dp0 is a historical dreg.