Maxim Integrated DS4830A Optical Microcontroller - Manual (Page 143)

DS4830A User’s Guide
143
SECTION 16 – GENERAL-PURPOSE TIMERS
The DS4830A has two identical 16-bit general-purpose timers. Each timer has the following,
• Two modes - Free synchronous and Compare
• Three Clock source selection options - Core clock, Peripheral clock and External clock
• 6 prescalers
• Interrupt feature in both modes.
Core Clock
00b or 01b
External Clock
11b
Clock Selection
MUX
Peripheral Clock
10b
Clock
Prescaler
GTPS[2:0]
GTV
15 0
0000h
15
GTC
0
RELOAD
Timer CLK
COMPARE
GTR
GTIF
GTIE
Next Timer Clock
Timer
Interrupt
Notes:
1. Free synchronous mode is a special compare mode in which the GTV is compared with 0xFFFF.
2. The GTV register is reset to 0x0000 when the GTR bit is set to ‘0’ (Timer off).
Compare Mode Block Diagram
Figure 16-1: Timer Functional Diagram
16.1 – Detailed Description
The DS4830A has two 16-bit programmable timer modules. Each timer module supports input clock selection
between Core, Peripheral and External clock sources. Each timer has two modes of operation i.e. free synchronous
timer and compare mode. The timer is controlled by the General Timer Reset (GTR) bit in the General Timer Control
Register (GTCN). When this bit is set to ‘1’, it enables the timer and starts counting up. When this bit is set to ‘0’, the
timer is stopped. Each timer has six prescalers selection feature. Using various prescaler and input clock options,
various timing loops can be generated.
16.1.1 – Timer Modes
Each timer has two modes of operation i.e. free synchronous timer and compare mode. The MODE bit in the GTCN
register selects the timer mode. The 16-bit free synchronous mode is configured by setting the MODE bit to 0. When
the Mode bit is set to ‘1’, compare mode is configured.
In free synchronous mode, the timer module begins counting up from 0x0000. When the General Timer Value
Register (GTV) value reaches to 0xFFFF, the GTIF interrupt flag is set to ‘1’ which generates an interrupt if enabled,
and the timer reloads the GTV register with 0x0000 at the next timer clock. The GTV register is a read only register
and it resets to 0x0000 when the timer is stopped. (GTR = 0).
In compare mode, the timer module begins counting from 0x0000 and when the value in the GTV register matches
the value in the General Timer Compare Register (GTC), the GTIF interrupt flag is set to ‘1 ‘ which generates an