Communication Line Interfaces; Functional-Level Operation - HP 3000 Series Installation And Service Manual

Principles of cperation
parallel from the INP Microprocessor and convert them into a
continuous serial stream for transmission. Simultaneously, they
·can receive a serial stream of data and control information and
assemble it into a series of parallel data bytes for the INP
Microp rocessor.
4-7. Communication Line Interfaces
The communication line interfaces,
Direct-connect, etc., translate
signals that are electrically and
the respective standards.
4-8. FUNCTIONAL-LEVEL OPERATION
such as RS232C, Bell DDS,
data and control lines into
mechanically compatible with
In the following typical message transmission sequence, a modern
telephone line is assumed as the communications medium. Refer-
ences are made to the functional areas, data paths, and service
request paths within the block diagram in figure
4-1. The data paths and service request paths being referenced
are identified in the diagram by circled numbers.
Initially, the HP 3000 has been powered up, and the previously
attached communication line is not yet operational. The process
of powering up invokes the ROM-resident control program. The
control program both resets the INP logic and verifies INP opera-
tion. The results of the operation verification are available to
the HP 3000 on request.
To initiate transmission, the system issues a control parameter
over the Hewlett-Packard Interface Bus (HP-IB) to the HP-IB
Interface of the INP, (1) • This action causes an interrupt bit
to be set, (2) , which interrupts the INP Microprocessor, (3)
The INP Microprocessor then reads the interrupt register, (4) ,
to determine which device is requesting service. Next, the INP
Microprocessor interrogates the HP-IB Interface, (5) , to
determine the nature of the service being requested (new control
word, new data word, etc.).
In this example, the control word read in (5) tells the INP
microprocessor to start transferring data words from the HP-IB
Inter face to the INP RAM for local buffer ing. Typically, the INP
reads a whole buffer or block from the HP 3000 before beginning
to transfer data over the data communication line.
The flows from the HP 3000 into memory are represented by (6)
and (7) in figure 4-1. Upon receiving a full block, the INP
Microp rocessor raises RTS, (8), and sets up an interrupt for
when the modem returns CTS. When CTS becomes active, an inter-
rupt is generated to the INP Microprocessor, (9) • The INP
Microprocessor then sends data from the INP RAM to the datacomm
4-4