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Part: AN459
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INTEGRATED CIRCUITS
AN459 8XC750 watering controller
Peious Yoseph and JeanPhilippe Chevreau 1997 July 10
Philips Semiconductors
Philips Semiconductors
Application note
8XC750 watering controller
Author: Peious Yoseph/JeanPhilippe Chevreau
INTRODUCTION
The 8XC750, as the lowest cost member of the Philips '51 family, is uniquely suited for high-volume consumer application. At less than $2 in volume, the chip enables a wide variety of feature-rich, value-priced products. One example of such a design, a '750 based watering controller (Figure 1), is described here. The watering controller can handle many residential and commercial applications, thanks to a variety of fully programmable features. The unit controls up to eight zones (i.e., valves) with independent programs, start times (day of week, hour, minute) and durations (199 minutes) accommodating nearly any watering schedule. The user interface, utilizing a high visibility 8-character alphanumeric display and four pushbuttons, is very easy to use. configuration is a simple matter of stepping through various menus and pushing INC or DEC pushbuttons (with auto-repeat) to set the desired value. Beyond these basics, the controller incorporates a number of other options designed to enhance versatility and ease of use. Battery back-up with explicit battery status (LED) and outage (flashing `:' in clock display) indicators insures the configuration is not lost during power failure. For at-a-glance status check, each zone has an activity LED that only illuminates if the valve is actually drawing power, easing diagnosis of cable and connection problems. Installation and service is further aided by a master valve power shutoff switch and status LED. Finally, the design accommodates an optional external humidity sensor input. Should excessive humidity be detected (as during rainfall), a pending watering program is automatically skipped.
AN459
8XC750 OVERVIEW
The 8XC750 (Figure 2) uniquely combines excellent performance with the cost, power consumption, and form factor requirements of consumer applications. In particular, the '750 represents the first step in a microprocessor upgrade path for previously mechanical, analog, and TTL-based controls. Thanks to the powerful instructions set, the on-chip code (1KB EPROM) and data (64-byte RAM) space is more than able to accommodate the processing complexity required of simple control applications. Similarly, the 19 I/O lines are up to the task of interfacing with the variety of small displays and keypads that comprise the user interface for many products. The '750 streamlined design delivers benefits of particular significance for entry-level applications. Active power consumption is low (Figure 3) and two reduced power modes (IDLE and POWER DOWN) extend battery life while minimizing power supply and thermal management concerns. Small 24-pin "skinny-DIP" and 28-pin PLCC packages are joined by the truly tiny SSOP package (Figure 4) to reduce product size and weight, paramount in portable products. Normally, such efficiency comes at the expense of performance, as in the case of 4-bit processors. Not so with the '750, which, running at up to 40MHz, delivers multi-MIPS throughout. The on-chip 16-bit auto-reload timer and dual external interrupt inputs allow a '750-based design to achieve sub-microsecond timing and control.
su00874
Figure 1. Watering Controller
1997 Jul 10
2
Philips Semiconductors
Application note
8XC750 watering controller
AN459
P0.0P0.2
PORT 0 DRIVERS VCC VSS RAM ADDR REGISTER RAM PORT 0 LATCH EPROM
B REGISTER
ACC
STACK POINTER PROGRAM ADDRESS REGISTER
TMP2
TMP1
ALU
PCON IE TH0 TL0 RTL RTH
TCON
BUFFER
PSW
INTERRUPT AND TIMER BLOCKS
PC INCREMENTER
PROGRAM COUNTER INSTRUCTION REGISTER
RST
TIMING AND CONTROL
DPTR
PD
PORT 1 LATCH
PORT 3 LATCH
OSCILLATOR PORT 1 DRIVERS X1 X2 P1.0P1.7 P3.0P3.7 PORT 3 DRIVERS
4 P3.4/A4 P3.3/A3 5
1
26 25
1 2
24 VCC 23 P3.5/A5 22 P3.6/A6 CERAMIC AND PLASTIC DUAL IN-LINE AND SHRINK SMALL OUTLINE PACKAGE 21 P3.7/A7 20 P1.7/T0/D7 19 P1.6/INT1/D6 18 P1.5/INT0/D5 17 P1.4/D4 16 P1.3/D3 15 P1.2/D2 14 P1.1/D1 13 P1.0/D0 Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14
PLASTIC LEADED CHIP CARRIER 11 12 Function P3.4/A4 P3.3/A3 P3.2/A2/A10 P3.1/A1/A9 NC P3.0/A0/A8 P0.2/VPP P0.1/OE-PGM P0.0/ASEL NC RST X2 X1 VSS 18 Pin 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Function P1.0/D0 P1.1/D1 P1.2/D2 P1.3/D3 P1.4/D4 P1.5/INT0/D5 NC NC P1.6/INT1/D6 P1.7/T0/D7 P3.7/A7 P3.6/A6 P3.5/A5 VCC 19
P3.2/A2/A10 3 P3.1/A1/A9 4 P3.0/A0/A8 5 P0.2/VPP P0.1/OEPGM P0.0/ASEL RST 6 7 8 9
X2 10 X1 11 VSS 12
SU00823
Figure 2. '750 Block Diagram
1997 Jul 10
3
Philips Semiconductors
Application note
8XC750 watering controller
AN459
60 22 20 18 16 14 I CC(mA) 12 10 8 6 4 2 MAX IDLE ICC6 10 MAX IDLE ICC6 TYP IDLE ICC6 0 4 8 12 16 16 20 24 28 32 36 40 20 TYP ACTIVE ICC5 40 MAX ACTIVE ICC
5
50
MAX ACTIVE ICC5
I CC(mA)
30 TYP ACTIVE ICC5
TYP IDLE ICC6
Frequency (MHz)
Frequency (MHz)
SU00313
Figure 3. '750 Power Consumption ICC vs. Frequency Maximum ICC, values taken at VCC max. and worst case temperature. Typical ICC values taken at VCC = 5.0V and 25°C. Notes 5 and 6 refer to DC Electrical Characteristics in the datasheet.
1997 Jul 10
4
Philips Semiconductors
Application note
8XC750 watering controller
AN459
SSOP24: plastic shrink small outline package; 24 leads; body width 5.3mm
SOT340-1
Figure 4. '750 SSOP Mechanical Drawing
1997 Jul 10
5
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