| 摘要 |
A high speed data bus system for communication among various functional units (10). The functional units are mounted in immediately adjacent connectors (25) on the backplane (Fig. 4) to define a populated section of effective characteristic impedance Z0' and one or two unpopulated sections of impedance Z0. A populated end of the transmission line (40) is resistively terminated with a resistance corresponding to Z0' (65) while the unpopulated end is terminated with a resistance corresponding to Z0 (67). The border between the populated and unpopulated sections is terminated with a resistance corresponding to 1/(1Z0'-1/Z0) (68), thus eliminating signal reflections. Driver gating circuitry (Fig. 9B) responsive to first and second data input signals, an enable signal, and a conditional inversion input signal performs multiple levels of gating with minimum of propagation delay. The preferred differential receiver (Fig. 10B) amplifies a relatively low level differential input signal and performs an exclusive OR function with a conditional inversion signal. To implement the indivisibility of transfers the control logic for each port includes screening circuitry (190) responsive to the state of the port's buffers (180), and further responsive to flags from the functional unit for selectively accepting or rejecting bus information, and further includes screening constraint circuitry (230) ensure that the port accepts all or none of the information that makes up the transfer. Depending on the flag, the rejection may be total, or may apply only to a designated class of transfers. |
