SX18AC/SO Parallax Inc, SX18AC/SO Datasheet - Page 10

• Manufacturer Part Number: SX18AC/SO
• Description: IC MCU 2K FLASH 50MHZ SO-18
• Manufacturer: Parallax Inc
• Series: SXr

Specifications of SX18AC/SO

• Core Processor: RISC
• Core Size: 8-Bit
• Speed: 50MHz
• Number Of I /o: 12
• Program Memory Size: 3KB (2K x 12)
• Program Memory Type: FLASH
• Ram Size: 137 x 8
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 18-SOIC
• Voltage - Supply (vcc/vdd): -
• Eeprom Size: -
• Data Converters: -
• Peripherals: -
• Connectivity: -

SX18AC / SX20AC / SX28AC
4.0 SPECIAL-FUNCTION REGISTERS
The CPU uses a set of special-function registers to con-
trol the operation of the device.
The CPU registers include an 8-bit working register (W),
which serves as a pseudo accumulator. It holds the sec-
ond operand of an instruction, receives the literal in
immediate type instructions, and also can be program-
selected as the destination register.
A set of 31 file registers serves as the primary accumula-
tor. One of these registers holds the first operand of an
instruction and another can be program-selected as the
destination register. The first eight file registers include
the Real-Time Clock/Counter register (RTCC), the lower
eight bits of the 11-bit Program Counter (PC), the 8-bit
STATUS register, three port control registers for Port A,
Port B, Port C, and the 8-bit File Select Register (FSR).
The five low-order bits of the FSR register select one of
the 31 file registers in the indirect addressing mode. Call-
ing for the file register located at address 00h (INDF) in
any of the file-oriented instructions selects indirect
addressing, which uses the FSR register. It should be
noted that the file register at address 00h is not a physi-
cally implemented register. The CPU also contains an 8-
level, 11-bit hardware push/pop stack for subroutine link-
age.
*In the SX18 package, Port C is not used, and address
07h is available as a general-purpose RAM location.
4.1 PC Register (02h)
The PC register holds the lower eight bits of the program
counter. It is accessible at run time to perform branch
operations.
© 1998 Scenix Semiconductor, Inc. All rights reserved.
00h
01h
02h
03h
04h
05h
06h
07h
Addr
Table 4-1. Special-Function Registers
INDF
RTCC
PC
STATUS
FSR
RA
RB
RC*
Name
Used for indirect addressing
Real Time Clock/Counter
Program Counter (low byte)
Holds Status bits of ALU
File Select Register
Port RA Control register
Port RB Control register
Port RC Control register
Function
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4.2 STATUS Register (03h)
The STATUS register holds the arithmetic status of the
ALU, the page select bits, and the reset state. The
STATUS register is accessible during run time, except
that bits PD and TO are read-only. It is recommended
that only SETB and CLRB instructions be used on this
register. Care should be exercised when writing to the
STATUS register as the ALU status bits are updated
upon completion of the write operation, possibly leaving
the STATUS register with a result that is different than
intended.
Bit 7-5: Page select bits PA2:PA0
Bit 4:
Bit 3:
Bit 2:
Bit 1:
Bit 0:
Bit 7
PA2
PA1
Time Out bit, TO
Power Down bit, PD
Zero bit, Z
Digit Carry bit, DC
Carry bit, C
000 = Page 0 (000h – 01FFh)
001 = Page 1 (200h – 03FFh)
010 = Page 2 (400h – 05FFh)
011 = Page 3 (600h – 07FFh)
1 = Set to 1 after power up and upon exe-
cution of CLRWDT or SLEEP instructions
0 = A watchdog time-out occurred
1= Set to a 1 after power up and upon ex-
ecution of the CLRWDT instruction
0 = Cleared to a ‘0’ upon execution of
SLEEP instruction
1 = Result of math operation is zero
0 = Result of math operation is non-zero
After Addition:
1 = A carry from bit 3 occurred
0 = No carry from bit 3 occurred
After Subtraction:
1 = No borrow from bit 3 occurred
0 = A borrow from bit 3 occurred
1 = A carry or borrow from the MSB of the
result occurred. For rotate (RR and RL) in-
structions, this bit is loaded with the low or
high order bit, respectively.
0 = No carry from the MSB as a result of
Add operation, or borrow as a result of
Subtract operation.
PA0
TO
PD
Z
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DC
Bit 0
C