TMS370 datasheet(7/63 Pages) TI

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TMS370CxCx

8-BIT MICROCONTROLLER

SPNS040B – NOVEMBER 1995 – REVISED FEBRUARY 1997

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251–1443

central processing unit (CPU) (continued)

status register (ST)

The ST monitors the operation of the instructions and contains the global interrupt-enable bits. The ST register

includes four status bits (condition flags) and two interrupt-enable bits:

D The four status bits indicate the outcome of the previous instruction; conditional instructions (for example,

the conditional jump instructions) use the status bits to determine program flow.

D The two interrupt-enable bits control the two interrupt levels.

The ST register, status-bit notation, and status-bit definitions are shown in Table 3.

Table 3. Status Register (ST)

7654

IE2

IE1

Reserved

RW-0

R = read, W = write, 0 = value after reset

program counter (PC)

The contents of the PC point to the memory location of the next instruction to be executed. The PC consists

of two 8-bit registers in the CPU: the program counter high (PCH) and program counter low (PCL). These

registers contain the most significant byte (MSbyte) and least significant byte (LSbyte) of a 16-bit address.

During reset, the contents of the reset vector (7FFEh, 7FFFh) are loaded into the program counter. The PCH

(MSbyte of the PC) is loaded with the contents of memory location 7FFEh, and the PCL (LSbyte of the PC) is

loaded with the contents of memory location 7FFFh. Figure 2 shows this operation using an example value of

7000h as the contents of the reset vector.

Memory

Program Counter (PC)

PCH

PCL

0000h

7FFEh

7FFFh

Figure 2. Program Counter After Reset

memory map

The TMS370CxCx architecture is based on the Von Neuman architecture, where the program memory and data

memory share a common address space. All peripheral input / output is memory mapped in this same common

address space. As shown in Figure 3, the TMS370CxCx provides memory-mapped RAM, ROM, input / output

pins, peripheral functions, and system interrupt vectors.

The peripheral file contains all input / output port control, peripheral status and control, EPROM, and

system-wide control functions. The peripheral file is located from 1000h to 107Fh and is logically divided into

seven peripheral file frames of 16 bytes each. Each on-chip peripheral is assigned to a separate frame through

which peripheral control and data information is passed.

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