Negotiation; Overview; Negotiation Procedure; Precautions - Citizen iDP-3221 User Manual

2.

Negotiation

2.1

Overview

Usually, the printer is started in Compatibility mode, which corresponds to the Centronics interface phase. When the
host intends to switch to the Nibble or Byte mode, it sends a request and negotiates with the printer. A general flow
of negotiations is given below.
1) The host sets the IEEE 1284 Active signal to High. In response, the printer moves into the Negotiation phase.
2) The printer replies whether it can execute the mode requested by the host.
3) The interface terminates the Negotiation phase and moves into the communication phase.
2.2

Negotiation Procedure

The negotiations proceed as follows:
1) In IEEE 1284 communication phase, the host and printer are in Compatibility mode by default. It remains in
Compatibility mode as long as the host recognizes the connected device as an IEEE 1284 compatible device.
2) To start negotiations, the host sets the communication mode request bit on the data path. (Event 0)
3) The host sets IEEE 1284 Active (nSelectln) to High, and HostBusy (nAutoFd) to Low. (Event 1)
4) The printer responds by setting PtrClk (nAck) to Low, nDataAvail (nFault) to High, Xflag (Select) to High, and
AckDatReq (PError) to High. (Event 2)
5) The host sets HostClk (nStrobe) to Low. In response, the printer latches the data of the communication mode
request bit. (Event 3)
6) The host sets HostClk (nStrobe) and HostBusy (nAutoFd) to High. (Event 4)
7) If the printer has communication data to send to the host, it sets AckDataReq (PError) to Low, nDataAvail
(nFault) to Low, and Xflag (Select) to the value corresponding to the communication mode. (Event 5)
Xflag: Nibble Mode: Low, Byte Mode: High
8) The printer sets PtrClk (nAck) to High to indicate that it is ready to read the status line. (Event 6)
9) If the printer has communication data to send to the host, the host moves into the Host Busy Available phase or
Termination phase, and then returns to the Compatibility mode.
10) If the printer has no communication data to send to the host, the host moves into the Host Busy Data Not
Available phase or Termination phase, and then returns to the Compatibility mode.
11) If the printer cannot support the communication mode requested by the host, it sets Xflag (Select) as follows:
When Nibble mode is requested:
When Byte mode is requested:
2.3

Precautions

1) The Negotiation phase is triggered with the rising edge of the IEEE 1284 Active signal sent by the host.
2) In Compatibility mode, the time when the negotiation process begins is, as a general rule, after the host sets
nStrobe to High and then the printer outputs an nAck pulse.
Once the nStrobe signal is set to High, however, the printer immediately moves into the Negotiation phase
when the high state of IEEE 1284 Active is detected, even if the nAck pulse has yet to be output or is being
output. In this case, if the printer has returned to Compatibility mode after Termination, no nAck pulse will be
output.
3) Negotiations can be entered from the Busy or Error state of the Compatibility mode. In this case, the printer
will not return to the Busy or Error state it was in before the negotiations, but will remain in the printer state it
was in after Termination.
4) If the host requested a communication mode that is not supported by the printer, it must move into the
Termination phase and return to the Compatibility mode.
Table 2.4.1 Definitions of Request Bits in IEEE 1284 Communication Mode
Bit
7
Request Extensibility Link
High
Low
Definition
Bit Values
Hex.
(76543210)
10000000 80H
Xflag
When In the
supported printer
High Low