This post presents an alternate implementation of SISAM hardware – a “COM2″ plug-in. It is designed for plugging in ahead of a bracket DB9 cable, usually used for accommodating a second serial port. This implementation uses a different MCU – PIC16F88, which allows the application to utilize 30% more RAM for the sampling buffer.
As practice has shown, simple level converter with -12V supply derived from DTR/RTS is not capable to work on high speed. Therefore I have made several tests on speed with the original PNP-based design and a RS232 line driver SN75150 and publish test results in this post. Test summary is given in Table 1.
This post describes how SISAM can be used to build a simple environment for automated testing of embedded applications.
SISAM uses RTS/CTS flow control for reading command and DTR flow control for sending acquired data. This means that PC should set RTS before sending commands and watch for CTS (e.g. use CTS sensitivity option). When PIC goes into data acquisition mode, it sends an ASCII string starting with Y4-MODE: followed with new mode description. This description can be directly used with mode command or with BuildCommDCB function.
SISAM – SImple SAMpler – is a simple PIC-based hardware for precision dual channel data acquiring with moderate resolution (up to 500 ksps in continous mode and up to 5 Msps for very short sequence). It uses USART and SSP for sampling signals and software routines for RS232 communication. USART is configured for synchronous master reception, while SSP is set for synchronous slave reception and is driven by USART clock via external circuit (wire).
In sampling mode signals are sampled on USART.RX and SSP.SDI pins. It timing mode it measures time between signal alternations on CC1 pin using CCP module. Acuired data is sent using RS232 protocol.
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This chapter describes SISAM Command Language, provides Command Language BNF and describes SISAM responses
SISAM Hardware schematic is given on Figure 1.
Besides the MCU PIC16F690 it includes a 20 MHz crystal and a RS232 matching circuit.