Compuprint 9058 Programmer Manual - Manual (Page 132)

The Parallel Interface
A78408098-003 C.3
• Nibble Mode
This mode provides an asynchronous, reverse (peripheral-to-host)
channel, under control of the host. In this mode, peripheral device
to host data bytes are sent as two sequential, four-bit nibbles using
the four peripheral-to-host status lines. These two modes cannot
be active simultaneously.
•
Byte Mode
This mode provides an asynchronous, byte-wide reverse
(peripheral-to host) channel based on eight data lines of the
interface for data and the control/status lines for handshaking.
Byte mode is under host control and it cannot be simultaneously
active with compatibility mode.
Operating Phases
The link protocol is mainly based on the following three phases:
• Negotiation Phase
This phase is activated always by the host, only when in
compatibility mode, and defines:
− whether a bidirectional link protocol can be established.
−
the handshaking mode as well as the communications mode to
be used.
− the device identification, if supported.
• Communication Phase
This phase is based on well defined handshaking rules which
depend upon the selected link mode.
• Termination Phase
This phase is initiated by the host and returns the interface to the
compatibility mode.