8087 Architecture

The 8087 is internally divided into two processing elements, the control unit and the numeric execution unit. The numeric execution unit executes all numeric instructions, while the control unit fetches instructions, reads and writes memory operands, and executes the 8088 control class of instructions.

The numeric execution unit executes all instructions that involve the register stack. These include arithmetic, comparison, transcendental, constant, and data transfer instructions.

The data path in the numeric execution unit is 80 bits wide (64 fraction bits, 15 exponent bits, and a sign bit), which allows internal operand transfers to be carried out at a very high speeds.

Environment Data

The environment data can be stored in memory for examination, or while another routine takes control, with the FSTENV, or FNSTENV instruction.

FLDENV reloads the 8087 environment data from memory. The environment data consists of seven words indicating the current state of the 8087.

• Control word

• Status word

• Tag word

• Instruction pointer (two words)

• Operand pointer (two words)

Environment data occupies 14 bytes when stored in memory. The format of environment data, when stored in memory with the FSTENV, or FNSTENV instructions, is shown below.

Environment Data Format¹

Control Word	+0
Status Word	+2
Tag Word	+4
Instruction	+6
Pointer 2	+8
Operand	+ 10
Pointer	+ 12

Save State

FSAVE/FNSAVE instructions writes the full 8087 state, (environment data plus the register stack) to the memory location defined by the destination operand.

Exception Pointers

The exception pointers consist of the instruction pointers and the operand pointers. Whenever the 8087 executes an instruction, it saves the instruction address and the instruction opcode in the exception pointers. If the instruction references a memory operand, the 8087 keeps the address of the operand.

An exception handler can be written to store these pointers in memory and get information about the instruction that caused the error.

Register Stack

Each of the eight registers in the 8087's register stack is 80 bits wide, and each is divided into three fields: the sign, the exponent, and the significant fields. This format correspond* to the 8087's temporary real data type that is used for all calculations.

All numeric values kept in the 8087 registers are held in the 80-bit, temporary real floating-point format, which is the same format as the 80-bit temporary real data type.

Two modes are available for addressing the stack registers. The first mode implicitly uses the top one or two registers. This mode does not require

¹ +0, +2, +4, ... , +12 are the address offsets of each word.

² The instruction and operand pointers together form the "Exception Pointers" part of environment data.

any addressing bits in the 8087 instruction. The other mode allows any other stack registers to be used together with the top of stack register. The top of stack, or other register, can be specified as the destination.

Notes:

numeric execution unit числовой исполнительный блок

sign знак

Tag word слово признака

pointer указатель

offset, смещение; сдвиг

save state состояние записи

destination пункт назначения; адресат

exception pointer указатель особой ситуации

reference ссылка; обращение

handler обработчик

significant field значащее/значимое поле

temporary временный; рабочий

IV. С помощью данной схемы переведите следующие предложения.

Схема условных придаточных предложений

Тип предложения	Придаточное условное предложение	Главное предложение
Изъявительное наклонение	Present Indefinite	Future/Present Indefinite
Переводится настоящим или будущим временем. Указывает на действие, относящееся к любому времени.	If he works hard, Если он будет усердно работать, If both types of connections are available	he will pass his exams. он сдаст экзамены it is normally better to use the parallel one.
Сослагательное наклонение	Past Indefinite/Past Perfect	should (would, could, might) + Infinitive или Perfect Infinitive без to

Переводится глаголом в прошедшем времени с «бы». Относит действия к прошедшему периоду времени, предшествующему моменту речи.

If he worked hard If he had worked hard Если бы он усердно работал,

he would pass his exams. he would have passed his exams. он бы сдал экзамены.

Условные предложения вводятся союзами: if – если, unless – если не, а также словами provided (that), providing (that), on condition (that), in case – при условии, что; если.

1. If the core were solid it would form a closed path of very low resistance.

2. If I were to see your experiment, I should get a clear idea of this phenomenon.

3. If errors in input occur, it may be possible to correct the input information on the spot, at once.

4. If a general term were to be identified as applying to the logic operations, it might be symbolic logic.

5. If we were to compare these data, our presentation would take a numerical form only.

6. If we were to employ this technique, we ought to update our equipment.

7. The process could be repeated, providing we wanted to receive the final results.

8. Provided that the replacement rate of the old equipment exceeded the normal rate of obsolescence, laboratories would be much more attractive for the students.

V. Переведите предложения на английский язык. Модель: