CDP1857CE

CDP1857C March 1997 4-Bit Bus Buffer/Separator Description The CDP1857C is a 4-bit CMOS non-inverting bus separator designed for use in CDP1800-series microprocessor systems. It can be controlled directly by a 1800-series microprocessor without the use of additional components. The CDP1857 is designed for use as a bus buffer or separator between the 1800-series microprocessor data bus and I/O devices. It provides a chip-select (CS) input signal which, when high (1), enables the bus-separator three-state output drivers. The direction of data flow, when enabled, is controlled by the MRD input signal. In the CDP1857, when MRD = 1, it enables the three-state bus drivers (DB0-DB3) and transfers data from the DATA-IN lines onto the data bus. When MRD = 0, it disables the three-state bus drivers (DB0DB3) and enables the three-state data output drivers (DO0-DO3), thus, transferring data from the data bus to the DATA-OUT terminals. The CDP1857 can be used as a bidirectional bus buffer by connecting the corresponding DI and DO terminals (Figure 1). The MRD output signal from the 1800-series microprocessor has the correct polarity to control the CDP1857 when it is used as I/O bus buffer/separator. Therefore, the 1800-series microprocessor MRD signal can be connected directly to the MRD input of CDP1857. See Function Table 1 for use of the CDP1857 as an I/O bus buffer/separator. The CDP1857C is supplied in 16-lead hermetic, dual-in-line ceramic packages (D suffix), and in 16-lead plastic ...