مدار مجتمع (آی سی) آی سی‌کاربرد ویژه

Product Attributes

Introduction

The Am2909A is a 4-bit wide sequencer intended for sequencing through a series of microinstructions contained in memory. Two Am2909As may be interconnected to generate an 8-bit address (256 words), and three may be used to generate a 12-bit address (4K words). The Am2909A can select an address from any of four sources: 1) a set of external direct inputs (D); 2) external data from the R inputs, stored in an internal register; 3) a 4-word deep push/pop stack; or 4) a program counter register (which usually contains the last address plus one). The push/pop stack includes certain control lines so that it can efficiently execute nested subroutine linkages. Each of the four outputs can be OR'ed with an external input for conditional skip or branch instructions, and a separate line forces the outputs to all zeros; the outputs are three-state. The Am2911A is an identical circuit to the Am2909A, except the four OR inputs and the R inputs are removed and the D inputs connect to the ADDRESS REG/HOLDING REG. The Am2911A is in a 20-pin, 0.3° centers package. The Am2909A and Am2911A are 4-bit slice sequencers which are cascaded to form a microprogram memory address generator. Both products make available to the user several lines which are used to directly control the internal holding register, multiplexer and stack. By appropriate control of these lines, the user can implement any desired set of sequence control functions; by cascading parts he can generate any desired address length. These two qualities set the Am2909A and Am2911A apart from the Am2910, which is architecturally similar, but is fixed at 12 bits in length and has a fixed set of 16 sequence control instructions. The Am2909A or Am2911A should be selected instead of the Am2910 under the following conditions: Address less than 8 bits and not likely to be expanded Address longer than 12 bits More complex instruction set needed than is available on Am2910