Filter
Top Products
23
CHAPTER 3 REGISTERS
3.4 Program Status (PS)
The program status (PS) is a 16-bit application-specific register existing in the CPU.
In upper byte of program status (PS), the upper 5-bit is the register bank pointer (RP)
and lower 3-bit is the direct bank pointer (DP). The lower byte of program status (PS) is
the condition code register (CCR). The upper byte of program status (PS), i.e. RP and
DP, is mapped to address 0078
H
. So it is possible to make read and write accesses to
them by an access to address 0078
H
.
■ Structure of Program Status (PS)
Figure 3.4-1 shows the structure of the program status.
The register bank pointer (RP) indicates the address of the register bank currently in use. The relationship
between the contents of the register bank pointer and actual addresses is as shown in Figure 3.4-2.
DP shows the memory area (direct bank) used for direct addressing and bit direct addressing. Conversion
from the operand address of direct addressing and bit direct addressing to the real address follows the
conversion rule shown in Table 3.4-1 by using DP.
The condition code register (CCR) has bits for indicating the result of operations and the content of transfer
data and bits for controlling the operation of the CPU in the event of an interrupt.
Figure 3.4-1 Structure of Program Status (PS)
Figure 3.4-2 Conversion Rule for Actual Address of General-purpose Register Area
PS
RP
RP
HI NZVC
1514131211109876543210
IL0, 1DP
DP CCR
RP
R4 R3 R2 R1 R0 b2 b1 b0
A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
Lower bits of OP code
Transaction address
"0"
"0"
"0"
"0"
"0"
"0"
"0"
"1"