The timing commands directly affect the way the modem device controls the radio module. Beware! If they
are set incorrectly then data errors or unreliable operation will result.
The default settings are a safe, conservative setup for a typical 50mS set-up time multi-channel transceiver.
For faster (usually single channel) radios the PREAM value can be reduced. Do not reduce this parameter
too far, as it must deal with the settling times of the receiver data recovery circuit as well as the transmitter
turn-on time.
The DELAY and TXOFF parameters are primarily concerned with optimum channel usage with intermittent
user data streams. DELAY is a duration between first byte received (into an empty buffer) and the
transmitter key-up, while TXOFF holds the transmitter on after a packet has finished sending.
If a user is controlling their serial data stream more closely, and sending data in discrete, well organised
bursts, then DELAY and TXOFF can be set to zero.
Addressing
The M48 data packet includes an address byte. It will only communicate with a unit set to the same address.
There are four receive addresses (of which ADR1 is usually set to zero as a 'broadcast' mode) and a
separate transmit address.
Multiple receive addresses can be useful for multiple node systems, and for setting up simple (manual
routing) repeater networks
COMMANDS
ADR1 aa
ADR2 aa
ADR3 aa
ADR4 aa
ADTX aa
ADDR aa
FUNCTION
set receiver address 1
set receiver address 2
set receiver address 3
set receiver address 4
set transmitter address
set rx address 1 to zero and set tx address and rx addresses 2, 3 and 4 to a
Notes:
1. aa is a two digit hexadecimal value (00 to FE). Address FF (255) is not permitted.
2. Address commands write to volatile memory. To transfer programmed addresses to the power-up
settings, the PROM command must be used.
3. As supplied: adr1 is zero, and adr2, adr3, adr4 and tx address are all set to 1.
Mode commands
Beyond it's usual 'transparent data' mode, the M48 can also operate in an 'extended' mode. In this case the
maximum packet size is reduced from 16 bytes to 14, and a 'burst identifier' word is included (obviously this
slightly reduces overall throughput).
On transmit, a different burst identifier is attached to each new packet. The receiving unit ignores the second
(and subsequent) packet with the same identifier. This allows a receiving M48 to ignore multiple copies of
the same data packet (as will be encountered in multiple transmission or repeater/network systems)
COMMANDS
MEXT
AKN
TRIES rr
TIMEOUT tt
STAF
FUNCTION
Extended mode (burst ID on, multiple transmissions set by TRIES)
The unit now operates in acknowledge/resend (extended) mode
Number of transmissions attempts allowed in AKN and MEXT modes
Duration of AKN resend timeout (tt x 0.41mS)
Operate as a store and forward repeater (with MEXT set, or not)
Notes: Variables rr and tt are all two digit hexadecimal values (00 to FF)
Extended mode (MEXT) is used with repeater systems. With TRIES set to two or more, this mode sends
each packet several times (increasing the chance of reception at extreme range).
Lastly, the M48 has an ' AKN/re-transmit ' mode. In this case, after each packet is sent, the receiving unit
sends back an knowledge message. If this message is not successfully decoded, at the transmitting end, it
will re-send the packet. The knowledge timeout period and the number of permitted re-tries are both user
programmable.
[ Do not use AKN mode with STAF repeaters. Timing conflicts occur ]
AKN mode provides the greatest data transfer reliability, although the overall data throughput is markedly
reduced.
Radiometrix Ltd, M48A Apps board Manual
page 7
RADIOMETRIX [ RADIOMETRIX LTD ]
