Solartron Mobrey 3595 4C, User Manual

Page: 41 / 128

3595 4C User Manual Part One Programming the 3595 4C Interface card
35952350 (CH03/AA)
3-13
3.4.7 Selecting the RAM pages
The Page Select Register , at location 0xFF, allows the Host PC to select another RAM page from RAM
Page 0. When the number of the required page is written into this register, the 4C Interface card moves the
RAM window to allow access to this page. A Page Select Register on the selected page, when read,
returns to RAM window to RAM Page 0. (See Section 3.2 page 3-3.)
3.4.8 Transmitting data to the IMP
The Transmit Register (Figure 3.5) allows the Host PC to communicate with the 4C Interface card when it
wishes to transmit data to an IMP. The data to be transmitted is written by the Host PC into RAM Page 1.
Sections X through Y describe the function of each Transmit Register.
0xE8
0xE9
0xEA
0xEB
0xEC
0xED
Bit 7 Bit 0
TXR TXE
TX Interrupt Enable
Destination Address
(Reserved)
TX Buffer Size (m.s.byte)
TX Buffer Size (l.s.byte)
Transmit
Control
Transmit
Registers
TXB TBK Not used
Figure 3.5: Transmit Register
Transmission control
The Transmit Control Register is used to control and give the status of transmissions made by the 4C
Interface card. The bit functions are as follows:
TXR Transmit Request. The Host PC sets the TXR bit to tell the 4C Interface card that the data on
RAM Page 1 is to be transmitted. Another transmit can be requested only when the TXB bit is
cleared by the card.
On completion of the transmission, the TXB bit is cleared. (This is a more precise indication of
transmission complete than the clearance of the TXB bit.)
TXE Transmit Error Flag. The 4C Interface card sets the TXE bit to indicate a transmission error.
TXB Transmit Busy. The 4C Interface card sets the TXE bit to indicate that transmission has started.
The bit is cleared after transmission ends; another transmit can then be requested.
TBK Transmit Break. The Host PC sets this bit to tell the 4C Interface card to transmit a break
character on the S-Net.
The break character resets every IMP on the network. It is primarily intended for resetting every
locally powered IMP, although it also resets those powered via the S-Net. When every IMP is
reset, the TBK bit state returns to ‘0’. A break character can be used to re-establish correct
system operation when there are transmit or receive errors.
Transmit or receive errors may be caused by removing an IMP, or replacing one, in an
operational system. Although this activity is sometimes necessary, and certainly will not
damage the IMP hardware, it is not recommended.