SX User’s Manual Rev. 3.1 26 © 2000 Scenix Semiconductor, Inc. All rights reserved. www.scenix.com Chapter 2 Architecture memory for indirect addressing. In this mode, the global register bank and Bank 1 through Bank F are
accessible. Bank 0 is not accessible.
For direct addressing (fr=01-0F), the value of “fr” itself specifies the register to be accessed, and the
FSR register is ignored. For this addressing mode, only the global register bank is accessible. To gain
access to any other bank, you must use either indirect or semi-direct addressing.
For  semi-direct  addressing  (fr=10-1F),  the  bank  number  is  selected  by  the  four  high-order  bits  of
FSR, and the register within that bank is selected by the four low-order bits of “fr.” In other words,
the register address is obtained by combining the four high-order bits of FSR with the four low-order
bits of “fr”. In this addressing mode, the low-order bits of FSR are ignored. Bank 0 through Bank F
are accessible, but the global register bank is not accessible. Figure 2-2 shows how register addressing works in the indirect, direct, and semi-direct modes. The 16 global registers are always accessible by direct addressing, regardless of what is contained in the FSR
register. The global registers are also accessible with indirect addressing, but they are not accessible
with semi-direct addressing. Of the 16 global registers, nine are special-purpose registers (RTCC, PC,
STATUS, and so on), and six are general-purpose registers. Location 00 is used for indirect address-
ing (INDF). All of the registers in Bank 0 though Bank F are general-purpose registers.
To change the contents of the FSR register, the program can either write an eight-bit value to the FSR
register or use the “bank” instruction. The “bank” instruction writes the three high-order bits (4, 5,
and 6) in the FSR register. Bit 7 of FSR is used to select the upper or lower “bank” of memory banks.
Thus,  to  change  from one upper  bank  to  another,  only  a  single  “bank”  instruction  is  required.  To
change  from  one  upper  bank  to  a  lower  bank,  the  “bank”  instruction  must  be  followed  by  “setb
FSR.7”.