## CERN Host Interface addressing The CERN Host Interface is a system of fast 32 bit wide parallel point&hyphen.to&hyphen.point links between BI based VAXes, FASTBUS and VME systems. On the VAX side, the module needed is a Digital Equipment DRB32 interface. This is 32 bit parallel interface for the VAX BI. It can be connected to another DRB32, or to the "HyperVIOR" VME module, or to the "CHIFC" FASTBUS module. When using the CHI, the same addressing syntax is used on the VAXes as on M680x0 systems. The medium name is "DRB". The communication facility is a standard transport service, so it works by one side declaring itself to be a named access point (TSAP), and then the other side making a connection by quoting that name. Typically (but not necessarily) it will be the RPC server which declares an access point name, and the client which connects to it. In this way, more than one client task (on the VAX) can access the same server. The access point name is an alphanumeric case insensitive string of a maximum of 32 characters. The syntax is similar to that used with DECNET or ISO transport protocol:- The format for declaring a server at access point "FRED" would be

    			*FRED.DRB

The asterisk "*" indicates that an access point should be established with the name "FRED", and any connections to that TSAP accepted. The TSAP name is mandatory, and has a maxuimum length of 32 characters. To refer to a package MYPACK2 on which is provided by that server, the client side would specify

    			MYPACK2@FRED.DRB

Notice there is no asterisk: the network address FRED.DRB means that this side should actively request a connection to an existing TSAP called FRED on the other side. In this case, therefore, the server must be started before the client. The CHI FASTBUS module has an RPC server permanently listening at access point "BOOT", so any server package which has been attached (see the list produced by the "PACKAGES" command) can be accessed from the VAX as

    		<packagename> @BOOT.DRB

The physical DRB device used by the RPC system is defined by the logical name DRB_Device. This may be set up for you by the system manager, or by a setup command file which you run from your login.com file to specify which CHI you are using. Alternatively, on the VAX, you can override the device name by specifying it before the TSAP name:

    	$ DEFINE RPC_CLIENT_NAME *UQA0:FRED.DRB

### 16 bit interfaces: DRQ and DRE&hyphen-11 When using a microvax or VAX without a BI (Backplane Interconnect), the same software exists for 16 bit interfaces. The DRE&hyphen-11 is used on UNIBUS, and the DRQ&hyphen.11 on QBUS. In this case, the medium name is still .DRB as above but the logical name DRB_DEVICE is changed to indicate a UU: device rather than a UQ: device. For example,

    	$ DEFINE DRB_DEVICE _UUA0:
    	$ DEFINE RPC_CLIENT_NAME *FRED.DRB

    or
    	$ DEFINE RPC_CLIENT_NAME *_UUA0:FRED.DRB

### Run&hyphen.Time Libraries The VAX library to be used should be logical CHI$LIB, (file CHILIB.OLB), and not the usual RPC$LIB. The CHI$LIB library allows the use of DRB and DRQ interfaces, and also RS232, decnet and ethernet. On the CHIFC itself, the entire library is available in ROM, so one need only link to the symbol module CHI$ROM (file CHIMON.ROM). Ensure that you have the version corresponding to the ROMs in your CHI. On the Valet-Plus, the library for communication over the HVIOR is also in ROM, and the usual MONICA.ROM file should be used. For more information onthe CHIFC device, see the CHI User Manual.