AUTOMATIC ADDRESSING OF TELEMETRY CHANNELS

Abstract

To simplify telemetry software development, a design that elminates the use of software instructions to address telemetry channels is being implemented in our telemetry systems. By using the DMA function of the RCA 1802 microprocessor, once initialized, addressing of telemetry channels is automatic, requiring no software. In this report, the automatic addressing scheme is compared with an earlier technique that uses software to address telemetry channels. In comparison, the automatic addressing scheme effectively increases the software capability of the microprocessor, simplifies telemetry dataset encoding, eases data set changes, and may decrease the electronic hardware count. The software addressing technique uses at least three instructions to address each channel. The automatic addressing technique requires no software instructions. Instead, addressing is performed using a direct memory access cycle stealing technique. Application of an early version of this addressing scheme opened up the capability to execute 400 more microprocessor instructions than could be executed using the software addressing scheme. The present version of the automatic addressing scheme uses a section of PROM reserved for telemetry channel addresses. Encoding for a dataset is accomplished by programming the PROM with channel addresses in the order they are to be monitored. Software for one of our telemetry units was written using the software addressing scheme, then rewritten using the automatic addressing scheme. While 1000 bytes of memory were required by the software addressing scheme, the automatic addressing scheme required only 396 bytes. A number of prototypes using AATC have been built and tested in a telemetry lab unit. All have worked successfully.