Interface Selection; Prevention Hosts From Data Transfer Time-Out; Ieee1284.4 Protocol - Epson LX-300 Service Manual

LX-300+

1.3.4 Interface Selection

The printer has 2 interfaces; the parallel interface and serial interface. These
interfaces are selected manually by Default Setting or selected automatically.
Manual Selection
One of 2 interfaces can be selected by Default setting.
Automatic Selection
The automatic interface selection is enabled by Default Setting. In this
automatic interface selection mode, the printer is initialized to the idle
state scanning which interface receives data when it is powered on.
Then the interface that receives data first is selected. When the host
stops data transfer and the printer is in stand-by state for the seconds
specified by Default Setting, the printer is returned to the idle state. As
long as the host sends data or the printer interface is in busy state, the
selected interface is let as it is.
Interface State and Interface Selection
When the parallel interface is not selected, the interface gets into a
busy state. When the serial interface is not selected, the interface
sends XOFF and sets the DTR signal MARK. When the printer is
initialized or returned to the idle state, the parallel interface got into a
ready state, the serial interface sends XON and sets the DTR SPACE.
Caution that the interrupt signal such as a -INIT signal on the parallel
interface is not effective while that interface is not selected.

1.3.5 Prevention Hosts from Data Transfer Time-out

Generally, hosts abandons data transfer to peripherals when a peripheral is in
busy state for dozens of seconds continuously. To prevent hosts from this
kind of time-out, the printer receives data very slowly, several bytes per
minute, even if the printer is in busy state. This slowdown is started when the
rest of the input buffer becomes several hundreds of bytes. At last, when the
input buffer is full, the printer is in busy state continuously.

1.3.6 IEEE1284.4 protocol

The packet protocol described by IEEE1284.4 is supported on the parallel I/F.
Two function modes of IEEE1284.4 protocol, "Off" and "Auto" are available,
and one of them is selected according to the value of Default setting. (See
1.4.2.3 "Default Setting")
Product Description
Auto:
Communication is carried out in the conventional mode until a magic
string (1284.4 synchronous commands) is received. By receiving a
magic string, communication in IEEE1284.4 packet mode is started.
Off:
Communication is carried out in the conventional mode. A magic
string (284.4 synchronous commands) is discarded.
NOTE: The packet protocol of IEEE1284.4 allows a device to carry on
multiple exchanges or conversations which contain data and/
or control information with another device at the same time
across a single point-to-point link.
The protocol is not, however, a device control language. It
does provide basic transport-level flow control and
multiplexing services.
The multiplexed logical channels are independent of each and
blocking of one has no effect on the others. The protocol
operates over IEEE1284.
Interface Specifications
Revision A
23