TMS370 datasheet(7/50 Pages) TI

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TMS370Cx1x

8-BIT MICROCONTROLLER

SPNS012F – MAY 1987 – 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 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, status-bit notation, and status-bit definitions are shown in Table 3.

Table 3. Status Registers

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 contains 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 PC. 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 6000h 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 TMS370Cx1x 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 TMS370Cx1x provides memory-mapped RAM, ROM, data EEPROM,

I / O pins, peripheral functions, and system-interrupt vectors.

The peripheral file contains all I / O port control, peripheral status and control, EEPROM, EPROM, and

system-wide control functions. The peripheral file is located between 1010h to 104Fh and is divided logically

into four 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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