at85c51snd3b ATMEL Corporation, at85c51snd3b Datasheet - Page 70

• Manufacturer Part Number: at85c51snd3b
• Description: Single-chip Digital Audio Decoder - Encoder With Usb 2.0 Interface
• Manufacturer: ATMEL Corporation

Mode 0 (13-bit Timer)
Mode 1 (16-bit Timer)
Mode 2 (8-bit Timer with Auto-
Reload)
Mode 3 (Halt)
Interrupt
70
AT85C51SND3B
•
Table 80. Timer/counter 1 Operating Modes
Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 reg-
ister) with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register
(see Figure 32). The upper 3 bits of TL1 register are ignored. Prescaler overflow incre-
ments TH1 register.
Mode 1 configures Timer 1 as a 16-bit Timer with TH1 and TL1 registers connected in
cascade (see Figure 34). The selected input increments TL1 register.
Mode 2 configures Timer 1 as an 8-bit Timer (TL1 register) with automatic reload from
TH1 register on overflow (see Figure 36). TL1 overflow sets TF1 flag in TCON register
and reloads TL1 with the contents of TH1, which is preset by software. The reload
leaves TH1 unchanged.
Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt
Timer 1 when TR1 run control bit is not available i.e. when Timer 0 is in mode 3.
Each Timer handles one interrupt source that is the timer overflow flag TF0 or TF1. This
flag is set every time an overflow occurs. Flags are cleared when vectoring to the Timer
interrupt routine. Interrupts are enabled by setting ETx bit in IEN0 register. This
assumes interrupts are globally enabled by setting EA bit in IEN0 register.
Figure 41. Timer Interrupt System
M11
It is important to stop the Timer/Counter before changing modes.
0
0
1
1
M01
0
1
0
1
TCON.5
TCON.7
TF0
TF1
Mode
0
1
2
3
Operation
8-bit Timer/Counter (TH1) with 5-bit prescaler (TL1).
16-bit Timer/Counter.
8-bit auto-reload Timer/Counter (TL1).
Timer/Counter halted. Retains count.
IEN0.1
IEN0.3
ET0
ET1
Timer 0
Interrupt Request
Timer 1
Interrupt Request
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