XR16C872 Datasheet, PDF (42/60 Pages) Exar Corporation – DUAL UART WITH 1284 PARALLEL PORT AND PLUG-AND-PLAY CONTROLLER

XR16C872
DISCONTINUED
“NIBBLE MODE” SIGNAL DESCRIPTIONS
Signal
name
Signal
Type
Nibble mode
Name
Description
STROBE#
O
STROBE#
Not used for reverse data transfer.
AUTOFD#
O
HostBusy
Host nibble mode handshake signal. Set low to indicate host is
ready for nibble. Set high to indicate nibble has been received.
SELCTIN#
O
1284Active
Set high when host is in a 1284 transfer mode.
INIT#
O
INIT#
Not used for reverse data transfer.
ACK#
I
PtrClk
Set low to indicate valid nibble data, set high in response to
“HostBusy” going high.
BUSY
I
PtrBusy
Used for Data Bit-3, then Bit-7.
PE
I
AckDataReq Used for Data Bit-2, then Bit-6.
SELECT
I
Xflag
Used for Data Bit-1, then Bit-5.
ERR#
I
DataAvail#
Used for Data Bit-0, then Bit-4.
PD0-PD7
O
Not used.
NIBBLE Mode Data Transfer Cycle
1. Host signals ability to take data by asserting HostBusy low.
2. Peripheral responds by placing first nibble on status lines.
3. Peripheral signals valid nibble by asserting PtrClk low.
4. Host sets HostBusy high to indicate that it has received the nibble and is not ready for another nibble.
5. Peripheral sets PtrClk high to acknowledge host.
Rev. 1.00
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