Datasheet

57
AT8xC51SND1C
4109E–8051–06/03
Notes: 1. Reloaded from TH1 at overflow.
2. Reloaded from TH0 at overflow.
Reset Value = 0000 0000b
Table 62. TH0 Register
TH0 (S:8Ch) – Timer 0 High Byte Register
Reset Value = 0000 0000b
Table 61. TMOD Register
TMOD (S:89h) – Timer/Counter Mode Control Register
76543210
GATE1 C/T1# M11 M01 GATE0 C/T0# M10 M00
Bit
Number
Bit
Mnemonic Description
7GATE1
Timer 1 Gating Control Bit
Clear to enable Timer 1 whenever TR1 bit is set.
Set to enable Timer 1 only while INT1
pin is high and TR1 bit is set.
6C/T1#
Timer 1 Counter/Timer Select Bit
Clear for Timer operation: Timer 1 counts the divided-down system clock.
Set for Counter operation: Timer 1 counts negative transitions on external pin T1.
5M11Timer 1 Mode Select Bits
M11
M01 Operating mode
0 0 Mode 0: 8-bit Timer/Counter (TH1) with 5-bit prescaler (TL1).
0 1 Mode 1: 16-bit Timer/Counter.
1 0 Mode 2: 8-bit auto-reload Timer/Counter (TL1).
(1)
1 1 Mode 3: Timer 1 halted. Retains count.
4M01
3GATE0
Timer 0 Gating Control Bit
Clear to enable Timer 0 whenever TR0 bit is set.
Set to enable Timer/Counter 0 only while
INT0 pin is high and TR0 bit is set.
2C/T0#
Timer 0 Counter/Timer Select Bit
Clear for Timer operation: Timer 0 counts the divided-down system clock.
Set for Counter operation: Timer 0 counts negative transitions on external pin T0.
1
M10 Timer 0 Mode Select Bit
M10
M00 Operating mode
0 0 Mode 0: 8-bit Timer/Counter (TH0) with 5-bit prescaler (TL0).
0 1 Mode 1: 16-bit Timer/Counter.
1 0 Mode 2: 8-bit auto-reload Timer/Counter (TL0).
(2)
1 1 Mode 3: TL0 is an 8-bit Timer/Counter.
TH0 is an 8-bit Timer using Timer 1’s TR0 and TF0 bits.
0
M00
76543210
--------
Bit
Number
Bit
Mnemonic Description
7:0 High Byte of Timer 0