The Dallas DS1642 and DS1742 are time-keeping NVRAM devices. The DS1742 is Y2K compliant as it maintains a century field in a section of NVRAM that was previously reserved by Dallas in the DS1642.
The DS1x42 components model real time using a single pin that can be driven at a simulated interval representing one second. For modelling time in the target domain, a target scheduler may be used. For modelling real "wall-clock" time, the host scheduler may be used.
The DS1x42 have a "frequency test" function that involves toggling the least significant bit of the "seconds" register at an idealized frequency of 512Hz. When managed by a sid scheduler component, the actual frequency is around 500Hz.
| Behaviors | |
|---|---|
| timekeeping |
Whenever the clock input is driven, it is interpreted as a signal that one second has passed. An internal counter is incremented and all the time-related registers are recomputed. The counter is accessible by the epoch-time attribute. |
| frequency testing |
When the clock-control and clock-event pin-pair is connected to an external scheduler, the DS1642 standard "test bit" is toggled at an approximate simulated frequency. |
| register access |
The DS1642/DS1742 control registers and 2048-byte NVRAM are accessed across the read-write-port bus for byte-wide operations. The control registers are also exposed as attributes. This family of parts includes 2KB of non-volatile RAM. This component does not explicitly model this memory. Instead, it interacts through the memory-bus accessor with an external memory like hw-memory-ram/rom-basic. |
| SID Conventions | ||||||||
|---|---|---|---|---|---|---|---|---|
| functional | supported | - | ||||||
| save/restore | supported | - | ||||||
| triggerpoints | supported | They support setting triggerpoints on the state of data with the following names:
| ||||||
Related components
The 2KB of non-volatile memory included in these parts is not explicitly modeled by this component. Instead, it uses the "memory-bus" accessor to interact with an external memory like hw-memory-ram/rom-basic:
new hw-memory-ram/rom-basic nvram set nvram size 2048 connect-bus rtc memory-bus nvram read-write-port
In order to enable the "frequency test" function, you need to couple an external scheduler to this component. The following is an example of how to configure such a connection between a scheduler and the DS1742 component:
new sid-sched-host-accurate sched new hw-rtc-ds1742 rtc set sched num-clients 2 set sched 0-regular? 1 set sched 0-time 1000 # 1 sec connect-pin sched 0-event -> rtc clock connect-pin rtc clock-control -> sched 1-control connect-pin rtc clock-event <- sched 1-event
The hw-visual-clock component is a candidate gui for this component.
new hw-rtc-ds1742 rtc new hw-visual-clock rtc-gui relate rtc-gui "your rtc friend" rtc
These components rely on the accuracy and integrity of UTC time maintained by the host, as the time and date are initialized when the component is instantiated. The UNIX time() system call is used to acquire the time.
| pins | |||
|---|---|---|---|
| name | direction | legalvalues | behaviors |
| clock | in | - | timekeeping |
| clock-control | out | positive number | frequency testing |
| clock-event | in | - | frequency testing |
| buses | |||
|---|---|---|---|
| name | addresses | accesses | behaviors |
| read-write-port | 0x0 - 0x7FF | read/write byte-wide | register access |
| attributes | |||||
|---|---|---|---|---|---|
| name | category | legal values | default value | behaviors | |
| epoch-time | - | uint 32 | - | timekeeping | |
| year | register | 0..99 | - | register access | |
| month | register | 1..12 | - | register access | |
| date | register | 1..31 | - | register access | |
| day-of-week | register | 1..7 | - | register access | |
| hour | register | 0..23 | - | register access | |
| minute | register | 0..59 | - | register access | |
| second | register | 0..59 | - | register access | |
| state-snapshot | - | opaque | - | state save/restore | |
| tk xclock clone | - | "hw-visual-clock" | - | component gui | |
| accessors | ||
|---|---|---|
| name | accesses | behaviors |
| memory-bus | byte-wide | register access |
Same as hw-rtc-ds1x42
| attributes | |||||
|---|---|---|---|---|---|
| name | category | legal values | default value | behaviors | |
| century | register | 19..25 | - | register access | |
Dallas Semiconductor DS1642 data sheet, revision 031698; DS1742 data sheet, revision 091498. Available online, or in our local archives.