45111 Parallax Inc, 45111 Datasheet - Page 91

• Manufacturer Part Number: 45111
• Description: MANUAL FOR SX-KEY/BLITZ VER. 2.0
• Manufacturer: Parallax Inc

Specifications of 45111

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Parallax microcontroller
• For Use With: 70002PAR - GUIDE PROG THE SX MICRO -DAUBACH
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

The following code snippet demonstrates this:
10.2.4 Schmitt-Trigger
Every I/O pin in port B through port E can be set to normal or Schmitt-Trigger input. This can be
configured by writing to the appropriate Schmitt-Trigger register (ST_B, ST_C, ST_D and ST_E). The
I/O pins are set to normal input mode by default. Schmitt-Trigger mode can be activated for all pins,
regardless of pin direction but really matter only when the associated pin is set to input mode. By
configuring Schmitt-Trigger mode on input pins, the SX chip can be less sensitive to minor noise on the
input pins. , below, details the characteristics of Schmitt-Trigger inputs.
Schmitt-Trigger inputs are conditioned with a large area of hysteresis. The threshold for a logic 0 is 15%
of Vdd and the threshold for a logic 1 is 85% of Vdd. The input pin defaults to an unknown state until
the initial voltage crosses a logic 0 or logic 1 boundary. A voltage must cross above 85% of Vdd to be
interpreted as a logic 1 and must cross below 15% of Vdd to be interpreted as a logic 0. If the voltage
transitions somewhere between the two thresholds, the interpreted logic state remains the same as the
previous state.
; Logic Level Configuration
;
MODE $0D
MOV
MOV
MOV
MODE $0F
MOV
MOV
MOV
!ra,#%0000
!rb,#%11110000 ; Port B bits 4-7 to TTL, bits 0-3 CMOS
!rc,#%00001111 ; Port C bits 4-7 to CMOS, bits 0-3 TTL
!ra,#%1100
!rb,#%10110011 ; Port B bits 2,3,6 to output, all others input
!rc,#%11011110 ; Port C bits 0,5 to output, all others input
Figure 15 - Schmitt Trigger Characteristics
; Set Mode to Logic Level configuration
; Port A bits 0-3 to CMOS
; Set Mode to allow Direction configuration
; Port A bits 0-1 to output, bits 2-3 input
10 SX Special Features and Coding Tips
SX-Key/Blitz Development System Manual 2.0 Parallax, Inc. Page 91