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15.3.3.3 PLP_C – Pull-Up Resistor Enable Register
15 Appendix E: SX Data Sheet
PLP_C
76543210
RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0
A bit set to ‘1’ in this register disables the weak pull-up resistor on the corresponding port pin. A bit set
to ‘0’ in this register enables the weak pull-up resistor on the corresponding port pin.
15.3.3.4 ST_C – Schmitt-Trigger Enable Register
ST_C
76543210
RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0
A bit set to ‘1’ in this register disables the Schmitt-Trigger input on the corresponding port pin. A bit set
to ‘0’ in this register enables the Schmitt-Trigger input on the corresponding port pin.
15.3.4 Port D and E Registers (SX48/52)
The SX48/52 devices have two additional 8 bit ports, called Port D and Port E. Their configuration
registers are similar to the Port C configuration registers. Please refer to chapter 15.3.3 for the details.
15.4 Control registers
There are three registers that configure the SX: MODE, OPTION, and Fuses. These registers allow the
user to configure the SX in many ways. MODE and OPTION are run-time readable and writable while
Fuses is written to only at program time.
15.4.1 Mode register (SX20/28)
The MODE register (simply called M in SX-Key mnemonics) is a run-time readable and writable register
used to select the configuration registers for port operations.
MODE
76543210
0 0 0 0 M3 M2 M1 M0
When a port configuration instruction is executed, such as MOV !RA, #1, the value of the MODE
determines exactly which type of port configuration register will be written to. The right 4 bits in this
register are set to ‘1’ on power up. Below is an example detailing how the MODE register is used.
SX-Key/Blitz Development System Manual 2.0 • Parallax, Inc. • Page 171