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INTERNAL SPECIFICATIONS
65
4.4 Special Function Registers (TCON, SCON,.... ACC, B)
4.4.1 Outline
As can be seen from the configuration shown in Table 4-6, the MSM80C154S/ MSM83C154S
special function registers consist of 27 8-bit registers.
Special function registers can be accessed (R/W) by either data addressing or bit addressing.
All 27 registers can be specified by data addressing. 13 registers (P0, P1, P2, P3, TCON,
T2CON, SCON, IE, IP, PSW, ACC, B, and IOCON) can be specified by bit addressing.
If a register which does not exist at the data address is accessed when a special function
register is used, the read data becomes 0FFH. And when data is written, none of the registers
in the CPU are effected at all. Note, however, that since a jump is always executed when a
bit test instruction which results in a relative jump at data condition “1” is executed, make sure
that no instruction is executed for a register which does not exist.