PicStic^™ Summary

FEATURES

DESCRIPTION

PicStic is a low-cost, industrially oriented controller on a 0.85-square-inch SIP (PicStics are manufactured both with and without pins). Including options, PicStic incorporates digital inputs and outputs, analog inputs, real-time monitoring, power-input regulation, and serial communication (provided through software) in a single module. PicStic can be used independently or networked together.

PicStic offers both compatibility and improved performance and comes in three versions: PS1, PS2, and PS3. The PS1, PS2, and PS3 are all pin-compatible with the Parallax BASIC Stamp I.

The PicStic1 is a straight one-for-one programmable replacement for the BS1. The PicStic2 has all the features of the PicStic1 plus a real-time clock/calendar that keeps time in terms of the year, month, day of the month, day of the week, hour, minute, and seconds. The clock always runs while the PicStic2 is powered. An optional 3-V lithium battery maintains the clock when power is off. The battery, which is approximately 0.6" in diameter, can be mounted on the front or back of the PicStic2.

The PicStic3 has all the features of the PicStic1 plus a 2-channel, 12-bit ADC. The compilers contain library routines for reading the ADC and real-time clock. While PicStic is BASIC Stamp I pin-compatible, you can program it in more than BASIC. Unlike the customized hardware of the BASIC Stamp, PicStic uses a generic reprogrammable PIC16F84 processor and a customized compiler. Additional features and improvements typically involve recompiling your program, not buying new hardware.

The single major advantage of PicStic is that you get an additional one (PS2) or two (PS1 and PS3) I/O lines and access to the four PIC16F84 interrupt sources when using assembly language (or an assembly-language call appended to PBASIC or C). With an ADC, interrupts, and 10 I/O lines, the PS3 provides a powerful little controller for cost-conscious applications.

Using the PBASIC compiler, PicStic is 100% Stamp I compatible. As a bonus, it's also at least 15 times faster for the same crystal speed. It has twice the typically available program space (see our separate comparison sheet (in "Frequent Questions About PicStic") for more details).

ABSOLUTE MAXIMUMS

PIN DESCRIPTIONS

1.0 PicStic Overview

PicStic is a low-cost, industrially oriented controller on a 0.85-square-inch SIP. At its core is a Microchip Technology PIC16F84 RISC processor which includes onchip RAM, EEPROM, and other features. Optional PicStic peripherals include an NJU6355 real-time clock and an LTC1298 A/D converter.

1.1 PIC16F84 Processor

The PIC16F84 is a high-performance, low-cost, CMOS, fully-static 8-bit microcontroller with 1 KB x 14 EEPROM program memory and 64 bytes of EEPROM data memory. Its high performance is due to instructions that are all single word (14-bit wide), which execute in single cycle (1 µs at 4-MHz clock), except for program-branches which take two cycles (2 µs).

The PIC16F84 has 4 interrupt sources and an 8-level hardware stack. The peripherals include an 8-bit timer/counter with an 8-bit prescaler (effectively a 16-bit timer) and 13 bidirectional I/O pins. The high-current drive (25 mA maximum sink, 20 mA maximum source) of the I/O pins helps reduce external drivers and therefore, system cost.

1.2 NJU6355 Real-time Clock

The NJU6355 series is a serial I/O real-time clock. It contains a quartz crystal oscillator, a shift register, a voltage regulator, a voltage detector, and an interface controller. The NJU6355 requires only four microprocessor bits for data transfer. The microprocessor receives data anytime it is required.

The operating voltage is 2.0­5.5 V. Consequently, the NJU6355 counts accurate time data, even during backup. (The clock can only be read or written to when VCC is >= 4.75 V.) Since current consumption during backup is less than 3 µA, backup can be done over a long period of time with a small battery.

1.3 LTC1298 A/D Converter

The LTC1298 is a micropower, 12-bit, successive approximation sampling A/D converter. It nominally consumes 350 µA of supply current when sampling at 11.1 kHz. Supply current drops linearly as the sample rate is reduced. The ADC automatically powers down when not performing conversions, drawing only leakage current.

The LTC1298 contains a 12-bit, switched-capacitor ADC, a sample-and-hold, and a serial port. It has a 2-channel input multiplexer and can convert either channel with respect to ground or the difference between the two. The reference input is tied to the supply pin.

2.0 PicStic Software

When it comes from the factory, the PicStic has no software on the board itself. Code is developed using cross-development tools running on a desktop PC and is programmed into the PicStic for execution. There are several development environments from which to choose.

2.1 Assembly

Any cross-assembler capable of creating code for the PIC16F84 processor can be used to write assembly language programs for the PicStic. Microchip's assembler is available at no cost from their BBS and Web site. More information about the PIC instruction set and how to connect to the Microchip BBS may be found in the Microchip Data Book.

Other cross-assemblers are available including one from Parallax that enhances the PIC instruction set with one more familiar to 8051 programmers. Contact Parallax for more information.

A cross-assembler also comes with the Micromint PBASIC package.

2.2 PBASIC

Micromint's PBASIC compiler allows the use of BASIC Stamp-compatible programs on the PicStic, but with much higher execution speed. PBASIC also provides the capability to include custom assembly language routines for time-critical tasks.

Contact Micromint for more information about PBASIC.

2.3 C

The integrated C development environment gives developers the capability to quickly produce efficient code from an easily maintainable high-level language. The compiler includes built-in functions to access the PIC hardware such as READ_ADC to read a value from the ADC. Discrete I/O is handled by describing the port characteristics in a PRAGMA. Functions such as INPUT and OUTPUT_HIGH properly maintain the tristate registers. Variables including structures may be directly mapped to memory such as I/O ports to best represent the hardware structure in C. The microcontroller clock speed may be specified in a PRAGMA to permit built-in functions to delay for a given number of micro- or milliseconds. Serial I/O functions allow standard functions such as GETC and PRINTF to be used for RS-232-like I/O. The hardware serial transceiver is used for applicable parts when possible. For all other cases, a software serial transceiver is generated by the compiler. The standard C operators and the special built-in functions are optimized to produce very efficient code for the bit and I/O functions normally required for these microcontrollers.

Functions may be implemented inline or separate. Function parameters are passed in reusable registers. Inline functions with reference parameters are implemented efficiently with no memory overhead.

During the linking process, the program structure including the call tree is analyzed. Functions that call one another frequently are grouped together in the same page. Calls across pages are handled automatically by the tool transparent to the user. RAM is allocated efficiently by using the call tree to determine how locations can be reused.

2.4 Fuzzy Logic

Information to be included in next datasheet revision.

3.0 Programming the PicStic

The PicStic uses Microchip Technology's PIC16F84 EEPROM microcontroller which can be reprogrammed hundreds of times. These programs can be created by a number of sources. Assembly-language programs can be written in Microchip's native instruction set or Parallax's 8051-like instruction set. Compilers such as C, PBASIC, or fuzzy logic can be used as well. The single requirement of any programming environment is that the end result is a PicStic-compatible Intel hex file.

Programming a PicStic is done serially, involving only five signal connections. The five signals are power (5 V), ground (0 V), and *MCLR (which must be pulled to +12 V), and port pins RB7 (serial data) and RB6 (serial clock).

The PicStic Development package includes a low-cost microEngineering Epic SE programmer which is plug-compatible with PicStic and needs no programming adapters. (Note: the Parallax BASIC Stamp programmer cannot be used for programming PicStic.) The PicStic can be programmed with most other PIC16F84 programmers by making a simple five-wire DIP-to-SIP adapter. The five signals from your programmer's 16F84 DIP programming socket are wired to a 14-pin PicStic SIP socket as shown in the table.

Most assemblers and compilers enable you to take advantage of a variety of 16F84 configuration options. These include code protection, powerup timer, watchdog timer, oscillator designation (PicStic uses the XT), and user programming of the 64 bytes of additional EEPROM data memory. Be aware that you may have to set these conditions on the compiler for proper PicStic programming.

For a more involved description of the 16F84 programming algorithm and technology, refer to the Microchip Data Book.

4.0 PicStic Hardware

We provide sample code for much of PicStic's hardware features. It is beyond the scope of this document to provide full details about each device. However, we have tried to include enough information to allow the programmer to develop code in other languages than that used for the sample code.

4.1 Serial Connections

PicStics have no specific pins for serial I/O. The compilers allow the user to designate the physical pin locations of serin and serout. While we recommend the use of a proper level-shifting serial interface, PicStic also works in other BASIC Stamp serial configurations.

4.2 PA3 and PA4

The PA3 and PA4 I/O lines are directly accessible from assembly language and C. However, additional assembly language routines are necessary to access these lines from PBASIC.

The following program demonstrates how to use the extra PicStic I/O bits. PicStic1 and PicStic3 have PA3 available, while all three PicStics have PA4 available.

PB0 controls the mode. When PB0=0, PA4 becomes an input and PA3 becomes an output. When PB0=1, PA3 becomes an input and PA4 becomes an output. In both cases, the output is set to the opposite of the input. PB7 outputs a 1200-bps serial message that indicates what is happening. Note that if you tie PA3 to PA4 with a 1-kilohm resistor, the output self toggles the input. The toggle speed is relatively slow due to the 1200-bps serial output routine.

Frequent Questions about PicStic

1. Is PicStic BASIC Stamp-compatible?

Using the PBASIC compiler, PicStics are 100% BASIC Stamp-compatible. If you have an existing BS1 program, it can be compiled using the PBASIC compiler and executed exactly as before (including time-related functions). The only exception to this rule is the DEBUG command. Because PicStic uses a compiler, interactive features like debug are not compiled with the program. PicStic is also hardware pin-compatible with the BS1. Of course, PicStic has more memory space and additional optional features you may want to take advantage of.

2. I need more execution speed than either the BS1 or BS2 have.

BASIC Stamps use a BASIC interpreter which executes the BASIC program line by line. When using PicStic's PBASIC or C compilers, the program is converted into fast assembly-language routines before loading onto the PIC. Compilers are inherently faster than interpreters.

For example, the PBASIC compiler is typically at least 15 times faster than the BS1 (10.5 times faster than a BS2) with some individual instructions which are as much as 100 times faster. It's quite possible that using PicStic and the PBASIC compiler could save having to go directly to assembly language when a regular Stamp application is too slow.

3. I'm using a BS2. Is it PicStic-compatible?

The answer is yes and no. Obviously, since the BS2 has 16 I/O pins and PicStic only has 8 (or 10), they can't be physically interchanged. Furthermore, the BS2 has some additional instructions to the BS1, like X-10 and DTMF. PBASIC 1.1 compiler is designed to be straight BS1-compatible with only the addition of the PicStic clock and ADC functions.

If you went to the BS2 merely because it executes faster and has more program space than the BS1, it's quite possible that a PicStic, which also runs faster and has more memory, might fit the bill more cost-effectively. Future versions of the PBASIC compiler will include BS2-specific instructions which can be run on PicStic along with all the normal BS1 instructions.

4. I have a Parallax BASIC Stamp development system. Can I use it?

No. Parallax Basic Stamps are interpreted BASIC devices, and their development system is a tokenized BASIC downloader. PicStics use an EEPROM-programmable processor with a compiled program. As a compiler rather than an interpreter, it requires different development software. In addition, because we are programming the PIC processor itself, PicStic uses an EEPROM programmer rather than a simple serial downloader.

So, yes, you'll need a PicStic development system to use PicStic with PBASIC. Of course, since PicStic is still 100% BS1-compatible, one of the best ways to develop code for it might be to continue using a regular BS1 with DEBUG and then use PicStics for the volume OEM application.

5. Just how generic is the PicStic? Must I always use PBASIC?

PicStic uses a PIC16F84 processor with optional ADC or RTC hardware. Even though it is packaged with a BS1 pin-compatible layout, it is still an EEPROM PIC, and it executes PIC assembly-language programs. PicStic can be programmed with any PIC EEPROM programmer capable of serial-mode programming. A variety of commercial PIC programmers can do this.

6. How fast is the PicStic ADC?

The LTC1298 12-bit ADC on PicStic has a faster conversion time than any program you might write to use the data from it. As a rule of thumb, the ADC can provide 1000 samples per second should you care to exercise it that often.

7. How much current can I draw from PicStic's onboard regulator?

PicStic incorporates a heftier regulator than the BS1. It is also reverse voltage protected, unlike the BS1. How much current you can draw from it for powering external devices is a matter of total power dissipation. At a 9-V input and 25°C operation, 100 mA of output current is typically available. See the chart provided for more detail.

8. PicStic is BS1-compatible, yet it has two more I/O lines. Why?

PicStic has the same eight general-purpose I/O lines as the BS1 supported in PBASIC. Because it is an EEPROM PIC and not a serial programmed BS1, the two programming lines are no longer required. One of them (pin 4) is always available, while the other (pin 3) is shared with the RTC. PBASIC 1.1 compiler directly addresses the original eight I/O lines but not the extra two. Future versions will address these lines directly. For now, using these two I/O lines must be done with assembly-language code called from BASIC. The spec sheet explains this simple procedure.

9. Does PicStic support interrupts?

Yes. Provided you are using assembly language or an assembly-language call from PBASIC or C, you have access to the four 16F84 interrupt sources.

PicStic Comparison Chart