Capabilities

SISAM 88 – provides the same set of capabilities as SISAM 690 (differences are underlined/strikethrough):

• S – Sampling single logical channel – RB2 RB5 up to 500 ksps (kilo sample per sec)
• X – Sampling dual logical channels RB2, RB1 RB5, RB4 up to 200 ksps per each channel
• J – Limited buffered sampling sole channel @ 5 Msps (2560 1920 samples via internal buffer)
• M – Measuring pulse timing on RB3 RC5 up to 12 kHz average,
• o – drive (trigger) four five output pins right before (0.8us) sampling starts
• O – drive (trigger) four five output pins immediately and/or in a sequence (20 us per data byte)

In addition to mentioned above, SISAM can be used as a variable frequency generator (VFG). With the current firmware – as a side effect of S command (a separate command is planned for upcoming firmware updates)

System requirements

• High-speed serial port (such as SerialXP)
• Triple power supply (+5VDC, +12VDC, -12VDC)

Schematics

SISAM88 hardware schematic is given on Figure 1. It includes

• MCU PIC16F88 (U1)
• 20MHz crystal (X1)
• RS232 level converter, build up on SN75150 line driver (U2), current-limiting resistors R1-R3, R6, a Zener diode D1 that prevents RA5/VPP from being pulled up to +12V.
• Current-limiting resistors R4, R5 on input
• Four connectors J1-J4.

J2 is an angled 10 pin male IDC header identical to a COM2 connector on the motherboard. J1 is an angled female IDC header mating with the COM2 connector. J3 is an angled 4 pins header mating with Mini-Molex power connector (FDD power). J4 is a 6 pins header compatible with your ICSP programmer (for example PICkit2).

Actuator outputs are connected to RA0-RA3.
Wire RB4-RB5 delivers clock from EUSART to SSP. RB4 also serves as VFG output.

External connectors

Power – it is an altered FDD power connector. 12V ground header is pulled out of it and another header inserted instead. This header is wired to -12VDC.

Bracket DB9 – it is a standard COM2 bracket cable. In this design it is used as an input/output connector for connecting probes. Pin 5 on this connector is still used for ground to make it compatible with RS232 cables that may have it connected to the chassis. It make safe connecting a regular RS232 cable.

Firmware

SISAM v1.1/88 Firmware is available for download.

Revision 1.1 includes the following changes
1. Fixed defect with improper speed estimation for command r02;X0;

Board

Figure 2 shows the board layout (Scale 1:2). Discrete parts, which are not shown on this layout, are surface mount on the soldering side. PCB layout is not yet ready.

The board has some space reserved for the future upgrades.

ICSP

PIC can be programmed in circuit; however, the device should be disconnected from power supply.

Pictures

DB9 bracket	SISAM 88 board	Cables connected	SISAM in place
		Notice altered FDD power connector

See also: More about SISAM; Simplescope; Overclocking COM port; Downloads

Overview

Experiments were made with four RS232 Level Converter designs:

1. PNP Transistor, parasitic -12V
2. PNP Transistor + JFET current source, parasitic -12V
3. PNP Transistor, external -5V supply
4. SN75150 – Dual RS232 Line Driver

Test environment:

• TTL output generated by SISAM in diagnostic mode
• Converter loaded with 1.5m shielded cable (C?‰?100-300pF) + PC USART (Winbond)

Data verification methods:

• watching and reporting framing error condition and
• comparing received data to expected

Test tools:

• SITEST ??“ sends commands to SISAM and forwards data to stdout
• LOOFI ??“ reads data from stdin and verifies the stream against the master pattern, made of the first count characters.

Command lines for tests are the following

SITEST /port=COM1 /count=640000 U03; > c:\temp\U03.txt
LOOFI /count=224 /file=c:\temp\U03.txt

SITEST sends U03 command to SISAM. This command turns SISAM in diagnostic mode and SISAM sends sequences of characters 0×20 to 0xFF using baudrate, specified in the command (U00 ??“ 115.2K, U03 ??“ 921.6K). SITEST saves data to file and aborts execution if a framing error is detected. Then LOOFI is used to verify data.

1. Hardware loop test In this test RX and TX wires were connected on the free cable end and test data were send with a terminal application. Test has passed 460.8K and has failed on 921.6K ??“ wrong data received.
2. PNP parasitic -12V Test has passed 230.4K and has failed on 460.8K with farming error. Oscilloscope has shown that falling edge is too sloping. I have tried to lower R1 and R2 and test has failed. I also tried to shorten the cable from 1.5 m to 0.3m and it did not make results any better.
3. PNP+JFET parasitic -12V As a variation of previous design, I have replaced R2 with a 10mA current source made on BF245A. This did not make results any better. My explanation to this ??“ parasitic power is not a good power supply to drive even small capacitive load at that high speed.
4. PNP external -5V In this test the circuit was powered with??“5V external power supply. R1 and R2 were varied from 1K to 100 Ohm. The best results were achieved with speed R2=360 and R1=10K – Test has passed 460.8K and has failed on 921.6K with framing error. These resistor values cannot be used with parasitic power, because transistor’s collector current (Ic?‰?30 mA) is higher than can be derived from a single COM port line.
5. PNP+JFET external -5V This design I did not try because it needs another type of JFET with IDSS current 30mA and I did not have it handy.
6. SN75150 SN75150 is a dual supply dual RS232 line driver. Despite SN75150 datasheet states maximal baud rate 120K, it works on 921.6K and the test has passed 921.6K. I tried to power it with +5V and -12V parasitic power and it did not work at all.

7. Summary on tests

Table 1

N/T – Not tested

6. Notes on driver selection

In this chapter I provide my motivation for driver selection.

I have looked for drivers in TI Interface Selection Guide. None of 1000 kbps drivers were available from local dealers (besides those drivers are not cheap). Therefore I decided to take a 120K driver and ‘overclock’ it. Considering that the current level is important for driving capacitive load, I limited my selection to dual supply chips. With these constraints I picked the smallest PDIP chip available locally and it happens to be SN75150. Its advantages: small footprint, very little overhead, level compatibility with PNP-based design, low price. Disadvantages ??“ necessity of dual power supply.

If dual power supply is not acceptable, you may try other drivers (such as SN75C3232, MAX3232, MAX232). I would appreciate if you share your results with me.

Overview

For developing applications with a long life cycle it is very important to ensure that a new release contributes no regression comparing to the previous release. This may become a challenge when an application provides number of capabilities, operates in number of modes or implements number of states. A common approach for addressing this challenge is to establish an automated test environment.

Figure 1 shows a typical automated test environment. It consists of

Batch Controller – a (software) component for running tests in a batch and aggregating overall batch result Test Tool – a component that executes single tests and produce test outputs Comparator – a component that compares test outputs against masters and reports discrepancies Test Cases Repository – a storage of test batches, test cases, test input data and masters Test Log Repository – a storage of test output data and test discrepancies

Figure 1

Typical sequence of events for automated testing:

• Actor uses Batch Controller to start a specific test batch
• Batch Controller reads test cases that constitutes the batch
• Batch Controller calls Test Tool for executing a test case from the batch
• Test Tool reads input test data for the specified test case, applies stimuli to the Testable Application, captures, preprocesses and records application responses
• Batch Controller, upon completion of a test case (all test cases), calls Comparator to compare a test output to a corresponding test master.
• Comparator compares test output and master, writes discrepancies (if any) and signals success/failure
• Batch Controller, upon completion of all test cases, aggregates test results and signals a batch result (success/failure) to the Actor.

A simple test environment

A simple environment for automated testing can be implemented as the following

Test Tool

To use this simplest automated test environment for testing embedded applications, the Test Tool should be a command-line utility, capable to apply stimuli to the testable application and capture the application response to a file.

SISAM & SITEST

SISAM is PIC-based application capable to accept commands via RS232, actuate pins according to the command, acquire data from one or two channels and send acquired data via RS232. SITEST is a command line interface to SISAM. It accepts a sequence of characters from the command line, sends these commands to SISAM and writes data to standard output. These features make SISAM a good candidate for simple testing environment. Figure 2 shows architecture diagram for a test tool build on SISAM and SITEST.

Figure 2

Filters

Due to nature of embedded applications acquired data may vary from run to run even for valid runs. This variability is very application specific; it may make impossible output-to-master comparison, and thus may easily bury the idea of automated testing. To address this issue, acquired data should be filtered and coarsened to the level at which all valid runs would produce identical outputs while invalid runs would still have some difference in the output data. Such a filter should be a command line utility that reads from standard input and writes to standard output. Of course, writing a filter requires additional efforts, however, from authors’ experience, implementing a simple filter does not require any significant efforts.

Function Generators

SISAM is only capable to provide static stimuli for a period of data acquisition. Therefore, if the test conditions require some alternating stimuli applied in parallel with data acquisition, a "function generator" can be used in conjunction with SISAM. A "function generator" is an embedded application that accepts a static input (function ID) and generates a variable function on output.

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.

PC should change the COM port mode as directed. Since the mode description contains rts=off dtr=on, DTR will be set SPACE signaling that PC is ready to receive acquired data.

PC stops Data acquisition by setting DTR to MARK and restoring 115200 baud rate.

If during data acquisition PIC encounters an error, it signals a BREAK, e.g. holds RX in SPACE until PC sets DTR to MARK. PIC does not leave error state until PC holds RTS MARK, therefore, to recover from error state, PC should restore baud rate 115200, set RTS to SPACE and read error message.

When data acquisition is performed with sync flag and PC needs to break waiting, it should alter TX line. If CTS sensitivity option is applied to COM port, WriteFile to the port will not succeed, SetCommBreak should be used instead. After this PIC will enter a error sate which should be cleared as stated above.

Initial state

PC opens port for normal operation: baud=115200 parity=N data=8 stop=1 octs=on dtr=off rts=of

Sending a command to SISAM

PIC is in IDLE state 1. PC sets RTS=SPACE 2. PIC confirms by setting CTS=SPACE 3. PC sends commnd(s) 4. PIC sets CTS=MARK 5. PC continues transmission 6. PC completes transmission 7. PC sets RTS=MARK 8. 2 ms timeout 9. On either of (7) or (8) PIC accepts command 10. PIC sends new COM port mode 11. PC changes COM port mode 12. PC signals START by setting DTR=SPACE PIC is in WAIT state 13. PIC sends data PIC is in ACQUIRE state 14. PC signals STOP by setting DTR=MARK 15. PIC stops transmission 16. PC restores COM port mode PIC is in IDLE state

Output stream format

PIC sends acquired data as described below

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.

Schematic

Current version is build for PIC16F690. Hardware schematic is given in this post.

Capabilities

SISAM has a terminal-like console interface with a small set of ASCII-based commands and produces human readable and computer friendly responses.

SISAM – provides the following capabilities

• S – Sampling single channel – RB5 up to 500 ksps (kilo sample per sec)
• X – Sampling dual channel RB5, RB4 up to 200 ksps per each channel
• J – Limited buffered sampling sole channel @ 5 Msps (1920 samples via internal buffer)
• M – Measuring pulse timing on RC5 up to 12 kHz average,
• o – drive (trigger) output pins right before (0.8us) sampling started
• O – drive (trigger) output pins immediately and/or in a sequence (20 us per data byte)
  (two sequential commands Oxx;Oxx have interval approx 440 us – 436.6 + delay on PC USART)

Command language capabilities:

• executing all commands via ASCII/RS232 console
• command data is passed as hexadecimal digits

Communication capabilities

• RTS/CTS driven RS232 communication @ 115.2 kbps
• Parasitic -12V power RS232 matching circuit
• 32 bytes long RS232 reception buffer
• Data transfer mode operates on 115.2, 230.4, 460.8 and 921.6 kbps
• Best data transfer speed is selected by SISAM and reported via console
• Data transfer is driven by PC via DTR signal

System requirements:

To achieve high speed sampling rate, your COM port must be overclocked to the highest possible speed. Please follow this link to details on port overclocking. Table 1 lists maximal sampler resolution for possible baud rates.

Table 1. Maximal resolution versus baud rate

Applications

Sisam is designed for use in Simplescope and A Simple Environment for Automated Testing .

See details on Hardware for PIC16F690, Hardware for PIC16F88, Protocol, Command Language; Downloads

Command Language Overview

SISAM supports the following commands

Command Language BNF

SISAM Response Syntax

Figure 1. SISAM Hardware Schematic

Channel 0 input is wired to RB5 and RC5, channel 1 – to RB4.
Actuator outputs are connected to RC0-RC4 (wirings are not drawn on this schema).
Wire RB6-RB7 delivers clock from EUSART to SSP.

RS232 matching circuit

It is implemented on discrete elements and does not require -12V supply.
Inputs (RTS/DTR/RX) are implemented with current limiting resistors 100K. This design makes SPACE equal to logical "1" and MARK – to logical "0".
Outputs (TX/CTS) are implemented with discrete inverters built on PNP transistors V1, V2 and current limiting resistors. With this design SPACE is set by driving output pin to "0" and MARK – to "1". Output level inversion is performed in the firmware.
-12 V is derived from RTS or DTR line via V3, V4. This design requires at least one of these pins to be in MARK state.

Firmware

SISAM v1.0 Firmware is available for download

Board

I have used Microchip Low Pin Count Demo Board (LPCDB) that comes with PICkit 2.0.
The only modification required to the original LPCDB wiring – R7 has to be physically disconnected.
Because pins used for in-circuit programming are wired via 100K resistors, this design is safe to use with in-circuit programming. There is no need to disconnect the programmer to test the device.

Note on cabling.

Basically, inverters V1 and V2 are loaded with whatever cable you use to connect this device to your PC. This cable has some capacitance and this capacitance limits the communication speed. To work properly on high speed (460K and above) cable capacitance must not exceed 30 p. This may not be achievable with a regular RS232 cable 1.5 m long. Thus, keep the cable as short as possible or use a different design for RS232 matching circuit.

Please find test results on various RS232 Level Converters in this post