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and unpunched VFU channels in the SHOW LPT VFU display may be changed by depositing new values in the
PUNCHR and UNPCHR registers, respectively.
The FORMLN register holds the current VFU form length, and the VFU register array holds the content of the
current VFU tape. The register defaults to binary display, with channel 1 in the most-significant bit and channel 8 or
12 in the least-significant bit, depending on the VFU width. Elements 1-n correspond to VFU form lines 1-n, where
a 1 value indicates a punch, and a 0 value indicates a no-punch. Element 0 is the logical OR of elements 1-n, so a
1 value indicates that the channel is punched somewhere on the tape, and a 0 value indicates that the channel is
not punched.
4.9 12875A Processor Interconnect
The HP 12875A Processor Interconnect kit is used to communicate between the System Processor and the I/O
Processor of a two-CPU HP 2000 Time-Shared BASIC system. It consists of four identical 12566A Microcircuit
Interfaces and two interconnecting cables. One pair of interfaces is installed in adjacent I/O slots in each CPU, and
the cables are used to connect the higher-priority (lower select code) interface in each computer to the lower-
priority interface in the other computer. This interconnection provides a full-duplex 16-bit parallel communication
channel between the processors. Each interface is actually a bi-directional, half-duplex line that is used in the
primary direction for commands and in the reverse direction for status.
Two copies of the HP2100 simulator are run to simulate the SP and IOP. Each simulator contains an Inbound Data
interface assigned to the lower-numbered select code, and an Outbound Data interface assigned to the higher-
numbered select code. The IPLI and IPLO devices, respectively, simulate these interfaces. A pair of Telnet
connections simulates the interconnecting cables.
The IPLI and IPLO devices are initially disabled. A SET IPLI ENABLED command will enable both devices.
Attaching the IPLI device of one machine to the IPLO device of the other simulates connecting the cable. One copy
of the simulator listens for connections with these commands:
ATTACH -L {-W} IPLI <port-1>
ATTACH -L {-W} IPLO <port-2>
...where port-1 and port-2 are decimal numbers between 1 and 65535 that are not being used for other TCP/IP
activities. Adding the –W switch causes the command to wait up to 30 seconds for the connection. If the switch is
omitted, or if the connection is not established within 30 seconds, the simulator will poll for connections once it is
running.
The other copy of the simulator establishes connections to those ports with these commands:
ATTACH -C {-W} IPLO {<ip-address>:}<port-1>
ATTACH -C {-W} IPLI {<ip-address>:}<port-2>
If the optional ip-address is omitted, it defaults to localhost (127.0.0.1). Either copy may perform either operation,
but the operations must be done in matched pairs, as shown in this example:
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