GENERAL DESCRIPTION
The Model 2927 is a computer bus adapter for use with the IBM PC/AT, Compaq 386, or other fully compatible computer. It mounts in any available 16-bit expansion slot within the computer, and communicates with the host using a 16-bit data path.
This interface supports up to eight Model 3922 crate controllers via a Model 5843-Txyz 40-conductor, twisted-pair ribbon cable. (Order this cable separately.) Signaling on this bus is accomplished with RS-485 balanced-line drivers and receivers, giving high noise immunity and allowing an overall cable distance between the computer interface and the last 3922 of up to 90 meters (300 feet). The last 3922 on the Parallel Bus is terminated with a termination card (provided with the 3922).
Program transfers as well as DMA data blocks are supported by this interface. The DMA channel provides speed-efficient block transfers with the following modes of operation: Q-Scan, Q-Stop, Wait Until Q, and Stop on Word Count. Interrupt capability is provided. An interrupt can be generated by DMA Done or by a pending LAM. In response to a LAM interrupt, the host computer performs a parallel poll of the 3922s via the 2927. In response to the parallel poll, each 3922 requesting service asserts one of the eight data lines (i.e., Crate 5 asserts Data Line 5). This method increases the efficiency of the interrupt service routing in multicrate systems.
An on-board switch on the 2927 is used to select the base address in the PC’s I/O page. Strap options on the module select the DMA channel number as well as the interrupt request level for both the Done and LAM interrupts.
IBM PC/AT is a registered trademark of IBM Corporation