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May 1996
Order Number 272795-002
8XC251SA, 8XC
251SB,
8XC251SP
, 8XC251SQ
Embedded Micr
ocontr
oller
User
’
s Manual
1
2
3
4
5
6
7
8
...
457
458
8XC251SA, 8XC251SB
1
8XC251SP, 8XC251SQ
1
Embedded Microcontroller
1
Users Manual
1
User’s Manual
3
CONTENTS
5
Guide to This Manual
19
CHAPTER 1
21
GUIDE TO THIS MANUAL
21
Architectural
31
Overview
31
CHAPTER 2
33
ARCHITECTURAL OVERVIEW
33
251 Microcontroller Core
34
Figure 2-2. The CPU
37
A2604-02
38
Address Spaces
41
CHAPTER 3
43
ADDRESS SPACES
43
51 Architecture
45
A4133-01
46
A4385-01
48
• EA# = 1
51
Register File
54
Memory Address Space
54
• R10 is the B-register
55
MCS 51 microcontrollers
56
Table 3-6. Core SFRs
60
Table 3-7. I/O Port SFRs
60
Table 3-8. Serial I/O SFRs
61
Configuration
63
CHAPTER 4
65
DEVICE CONFIGURATION
65
A4237-01
66
8 Kbytes
66
16 Kbytes
66
access
71
A4218-02
74
Programming
81
CHAPTER 5
83
Table 5-1. Data Types
84
5.3.1.1 Register Addressing
87
5.3.1.2 Immediate
87
5.3.1.3 Direct
87
5.3.1.4 Indirect
88
251 Architecture
89
5.3.1.5 Displacement
90
PROGRAMMING
101
Interrupt System
103
CHAPTER 6
105
INTERRUPT SYSTEM
105
Interrupt Polling Sequence
106
Table 6-4. Level of Priority
111
Response Time = 4
116
6.7.2.3 Latency Calculations
117
Input/Output Ports
121
CHAPTER 7
123
INPUT/OUTPUT PORTS
123
Figure 7-2. Port 0 Structure
125
Figure 7-3. Port 2 Structure
126
Timer/Counters and
133
Watchdog Timer
133
CHAPTER 8
135
Interrupt
136
Overflow
136
Table 8-2. External Signals
137
A4112-02
140
8.6.2.1 Up Counter Operation
146
A4114-01
147
Clock-out Frequency
148
4 (65536 - RCAP2H, RCAP2L)×
148
A4116-02
149
Programmable
153
Counter Array
153
CHAPTER 9
155
PROGRAMMABLE COUNTER ARRAY
155
(16 Bits)
157
for mode
158
• No operation
159
A4163-02
160
A4164-01
162
A4165-01
164
A4166-01
165
A4161-01
166
Table 9-3. PCA Module Modes
168
Figure 9-9. CCAPM
169
Serial I/O Port
171
CHAPTER 10
173
SERIAL I/O PORT
173
A4123-02
174
Transmit
177
A2261-01
178
A4120-01
185
Minimum Hardware
187
Figure 11-1. Minimum Setup
189
MINIMUM HARDWARE SETUP
191
External
192
Clock Driver
192
First ALE
196
Special Operating
197
CHAPTER 12
199
SPECIAL OPERATING MODES
199
A4160-01
201
External Memory
207
Interface
207
CHAPTER 13
209
EXTERNAL MEMORY INTERFACE
209
• The chip is in idle mode
211
A4230-01
212
A2809-04
214
A2813-04
218
A5009-01
221
A5008-01
222
A4228-01
223
A4219-01
226
A4220-02
227
A4148-01
228
A4147-02
230
A4169-03
231
A4221-01
232
A4151-01
238
Programming and
239
Verifying Nonvolatile
239
CHAPTER 14
241
PROGRAMMING AND VERIFYING
241
NONVOLATILE MEMORY
241
A4122-02
245
A4129-01
246
Instruction Set
251
Reference
251
APPENDIX A
253
INSTRUCTION SET REFERENCE
253
51 Microcontrollers
256
257
Table A-8. Data Instructions
258
Table A-10. Bit Instructions
259
Table A-15. INC/DEC
262
Table A-17. Shifts
262
Table A-28. Flag Symbols
278
IF (A) < #data
294
IF (A) < dir8
294
← (WRj).b
373
Signal Descriptions
391
APPENDIX B
393
SIGNAL DESCRIPTIONS
393
Registers
401
APPENDIX C
403
REGISTERS
403
Table C-2. Core SFRs
405
Table C-3. I/O Port SFRs
405
Table C-4. Serial I/O SFRs
406
Table C-7. Register File
408
Glossary
437
GLOSSARY
439
Glossary-2
440
Glossary-3
441
Glossary-4
442
Glossary-5
443
Glossary-6
444
Glossary-7
445
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