SX18AC/SO Parallax Inc, SX18AC/SO Datasheet - Page 29

• 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: -

15.10.2 Page Jump Operation
When a JMP instruction is executed and the intended
destination is on a different page, the page select bits
must be initialized with appropriate values to point to the
desired page before the jump occurs. This can be done
easily with SETB and CLRB instructions or by writing a
value to the STATUS register. The device also has the
PAGE instruction, which automatically selects the page in
a single-cycle execution.
Note:“N” must be 0, 1, 2, or 3.
15.10.3 Call Operation
The following happens when a CALL instruction is exe-
cuted:
• The current value of the program counter is increment-
• The lower eight bits of the label address are copied into
• The ninth bit of the Program Counter is cleared to zero.
• The page select bits (in STATUS register) are copied
This means that the call destination must start in the
lower half of any page. For example, 00h-0FFh, 200h-
2FFh, 400h-4FFh, etc.
15.10.4 Page Call Operation
When a subroutine that resides on a different page is
called, the page select bits must contain the proper val-
ues to point to the desired page before the call instruction
is executed. This can be done easily using SETB and
CLRB instructions or writing a value to the STATUS reg-
ister. The device also has the PAGE instruction, which
automatically selects the page in a single-cycle execu-
tion.
Note:“N” must be 0, 1, 2, or 3.
© 1998 Scenix Semiconductor, Inc. All rights reserved.
ed and pushed onto the top of the stack.
the lower eight bits of the program counter.
into the upper two bits of the Program Counter.
STATUS<6:5>
STATUS<6:5>
STATUS<6:5>
PC<10:9>
PC<10:9>
PC<10:9>
PC<8>
0
JMP LABEL
JMP LABEL
PC<8:0>
PC<8:0>
PAGE N
CALL LABEL
PC<7:0>
- 29 -
15.11 Return Instructions
The device has several instructions for returning from
subroutines and interrupt service routines. The return
from subroutine instructions are RET (return without
affecting W), RETP (same as RET but affects PA1:PA0),
RETI (return from interrupt), RETIW (return that affects
W), and RETW #literal (return and place literal in W). The
literal serves as an immediate data value from memory.
This instruction can be used for table lookup operations.
To do table lookup, the table must contain a string of
RETW #literal instructions. The first instruction just in
front of the table calculates the offset into the table. The
table can be used as a result of a CALL.
15.12 Subroutine Operation
15.12.1 Push Operation
When a subroutine is called, the return address is
pushed onto the subroutine stack. Specifically, each
address in the stack is moved to the next lower level in
order to make room for the new address to be stored.
Stack 1 receives the contents of the program counter.
Stack 8 is overwritten with what was in Stack 7. The con-
tents of stack 8 are lost.
STATUS<6:5>
PC<10:9>
PC<8>
0
PC<10:0>
STACK 1
STACK 2
STACK 3
STACK 4
STACK 5
STACK 6
STACK 7
STACK 8
SX18AC / SX20AC / SX28AC
CALL LABEL
PC<7:0>
PAGE N
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