Data Sheet

4-Level FSK Modem Data Pump Page 31 of 47 MX919B PRELIMINARY INFORMATION

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Note: during this time the µC may

perform other functions, as the

µC variable 'STATE' is updated

by the interrupt service routine

Disable µC's MX919B Tx Interrupt Service Routine

Enable µC's MX919B Tx Interrupt Service Routine

Set µC variable 'STATE' to 0

Set the Mode Register IRQEN bit to '1'

Set the Mode Register IRQEN bit to '0'

Read the Status Register

Write a RESET task to the Command Register

Set µC variable 'IBLOCKS'

to the number of Intermediate blocks

to be transmitted

Ensure that the Control Register

has been loaded with

a suitable CKDIV value

Write a T24S task to the Command Register

Write 6 bytes of Symbol Sync

pattern to the Data Buffer

Ensure that the Mode Register

IRQEN, PSAVE and RXEYE bits are '0',

the TX/RX bit is '1',

and the INVSYM bit is set appropriately

Ye s

END

with error

END

START

'STATE' < 5 ?

BFREE bit = 1 ?

'STATE' = 5 ?

Figure 19: Transmit Frame Example Flowchart, Main Program

Notes

1. The RESET command in Figure 19 and the practice of disabling the MX919B’s

IRQ output when not

needed are not essential but can eliminate problems during debugging and if errors occur in operation

2. The CRC and TXIMP bits should be set appropriately every time a byte is written to the Command