D/Cas - Teac MT-20D-IO Maintenance Manual

"D/CAS"
3-4 Interface control (PCBA Interface Control)
The PCBA interface control (hereinafter, referred to as MTC) controls the
transfer of command/status and read/write data with the host system (here-
inafter, referred to as HOST), or performs data processing or tape position
control with respect to the PCBA drive control (hereinafter, referred to as
GMT) . The main functions of MTC are controlled by CPU (U9/80C85A micro-
processor), while the data system requiring high speed transfer is
controlled by DMAC (U7/82C37 DMA controller).
The data transfer between the individual blocks within MTC as shown in Fig.
301(a) is performed by DMAC in competition with CPU on the CPU bus (cycle
stealing mode). At this time, however, this system is programmed so that
the CPU bus is released to CPU once on every DMA cycle to prevent the CPU
bus from being occupied for a long time, when data transfer requests are
concentrated, thereby assuring the worst operating ratio of CPU.
Description is given below on the operation of each block of MTC (PCBA
interface control) shown in Fig. 301(a).
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