Digi NS9750 - Manual (Page 700)

O v e r v i e w
6 7 6 N S 9 7 5 0 H a r d w a r e R e f e r e n c e
Because the NS9750 functions only as a slave, it is not necessary to provide the
capability of driving any non-IEEE 1284 compliant commands back to the host.
Important:
The 1284 commands are not designed to be stored and passed along. To
store a non-IEEE 1284 command in the forward command FIFO, send an
RLE command of count one (
0x0
), followed by the command you want to
send. Both bytes must be transferred while
HostAck
is low and bit[14] of
the IEEE 1284 General Configuration register (see page 679) is set to 0.
IEEE 1284 negotiation
The negotiation process is a mechanism by which the host determines the capabilities
of the attached peripheral. The module can be programmed to interrupt the software
when the host begins negotiation. The module automatically completes negotiation
into byte, nibble, and ECP modes. The host uses an extensibility byte to communicate
to the module which mode is being negotiated into.
Warning:
During a negotiation into either nibble or byte mode, the behavior of the
pError
signal driven by the NS9750 is out of compliance with the IEEE 1284
standard. The
pError
signal does not match the value of
nFault
at event #6 of
the negotiation process.
Table 389 defines the extensibility byte values.
Extensibility byte Definition Description
1000 0000 Reserved Reserved
0100 0000 Reserved Reserved
0011 0000 Request ECP mode with RLE
0001 0000 Request ECP mode without RLE
0000 1000 Reserved Reserved
0000 0100 Request device ID using nibble mode Receive the device ID a nibble at a time
across the status lines.
0000 0101 Request device ID using byte mode Receive the device ID a byte at a time
across the data lines.
0001 0100 Request device ID using ECP mode
without RLE Receive device ID without ECP data
compression.
Table 389: Extensibility byte values