Econet Clocks
| About Clocks | BBC micro clock | Acorn Clock type 1 | Acorn Clock type 2 |
| SJ Research Clock | Acorn FileStore Clock | SJ Research Econet Bridge Clock | American Clock |
Econet Clocks
| About Clocks | BBC micro clock | Acorn Clock type 1 | Acorn Clock type 2 |
| SJ Research Clock | Acorn FileStore Clock | SJ Research Econet Bridge Clock | American Clock |
About Clocks
The purpose of an Econet Clock is not to tell the time. It is to transmit a signal to all stations on the network to allow them to synchronise the transmission and receipt of data. Without an Econet Clock, the network will not function.
The speed of the clock setting determines the speed of data transfer along the network. The are two phases to the clock's timing, the Mark and the Space. The Mark and the Space, when added together, produce the Period which indicates the speed of the clock.
Clock speeds are determined in microseconds and the mark duration should be lower than the space duration. In some clocks, the space is expressed as a multiple of the mark so it is impossible to set the space shorter than the mark. In other clocks the mark and space can be set independently so it would be possible to set the space shorter than the mark.
BBC Micro Clock
Issues 2 and 3 of the BBC micro motherboard contained provision within the Econet interface to generate a clock for the network. Click here to learn more.
Acorn Clock Type 1
This is the earliest of all Econet clock boxes. It comes in a two colour box with a beige lid and grey base and has only one Econet socket.
The Level 1 Econet Clock also reportedly produced a "symmetrical" clock signal, ie. the mark and the space duration were the same. This is not ideal because the data is transmitted during the space so half the time would be lost whilst the clock was in the Mark phase.
Click on the picture above to learn more about the Level 1 Clock.
Acorn Clock Type 2
 |
 |
 |
 |
The Acorn Clock type 2 is housed in a small black box with a power supply transformer. It has two Econet ports for attaching to the middle of a network. Inside are two sets of links to set the clock speed. The first set is the mark which may be 1 or 2 µseconds. The space is a multiplier of the mark, being 1, 2, 4 or 8. For a space of 8 µseconds, you might set the mark to 1 and the space multiplier to 8 or the mark to 2 and the space multiplier to 4. The mark added to the space gives the period, the clock speed.
SJ Research Clock
 |
 |
 |
This appears to be the most common type of network clock. Econet equipment produced by SJ Research is widely regarded as being superior to Acorn's own equipment. It is by far the most versatile of all clocks.
The SJ Research clock is housed in a black box with external power transformer and two Econet sockets for connecting to the network. Inside the clock are two sets of DIL switches for setting the Mark and the Period. With the SJ Research design, you do not set the mark and space to give the period, but you set the mark and the overall period. The space is then the period minus the mark.
The DIL switches provide mark settings of ⅛, ¼, ½, 1, 2 or 4µs. Any combination of switches can be used so the mark can be set between ⅛µs and 7⅞µs.
The period switches provide settings of ¼, ½, 1, 2, 4 or 8µs allowing a period range of ¼µs to 15¾µs.
Acorn FileStore
The FileStore E01 and E01S units have the ability to generate their own Econet clock. I have read in numerous places that this clock can interfere with the signal from another clock if present on the network, although I have never had any trouble running my FileStore and my SJ Research Econet Clock at the same time.
The FileStore clock signal is limited to a small number of stations on a short network. This possibly explains why the FileStore clock does not reach Station 200 or Station 201 on my network.
The clock is set in a similar way to the Acorn type 2 clock box. There is a set of links inside the FileStore which allow the mark to be set at 1 or 2µs with a space multiplier of 1, 2 or 4. This is less versatile than the Acorn clock box which has an additional multiplier of 8.
I think the FileStore clock can be disabled by removing all the link jumpers in case you wish to use a separate clock box on your network.
SJ Research Econet Bridge Clock
This is without doubt the most user-friendly of all the network clocks you might come across. The mark and period are set by pressing buttons on the front to cycle through the options in an on-screen menu. No opening up the device to mess about with links or DIL switches with the SJ Research Bridge!
Despite this, the settings cannot be refined quite as much as on the SJ Research Clock.
In addition to being able to set the mark and period in stages, there are predefined settings built into the menu for the BBC, Archimedes and MDFS.
The clock is generated on network B of the Bridge and can be disabled if not required. If another clock is present on network B, the Bridge will report an error and stop until either the Bridge clock is disabled or the other clock is disconnected or switched off.
American Econet Clock
Thinking I had written just about all there was to write about Econet Clocks, in August 2003 I discovered a completely new type of clock that I had never heard of or seen before. This is the American Econet Clock which is different in design and operation to the usual UK clocks. There is more about the American Clock here.