Quatech DS-3000 User Manual

Quatech DS-3000 User Manual Manual pdf 6 page image

F U N C T I O N A L D E S C R I P T I O NIII. 1 6 5 5 0 F U N C T I O N A L D E S C R I P T I O NT h e 1 6 5 5 0 i s a n u p g r a d e o f t h e s t a n d a r d 1 6 4 5 0A s y n c h r o n o u s C o m m u n i c a t i o n s E l e m e n t ( A C E ) . D e s i g n e d t ob e c o m p a t i b l e w i t h t h e 1 6 4 5 0 , t h e 1 6 5 5 0 e n t e r s t h echaracter mode on reset and in this mode will appear as a1 6 4 5 0 t o u s e r s o f t w a r e . A n a d d i t i o n a l m o d e , F I F O m o d e ,c a n b e s e l e c t e d t o r e d u c e C P U o v e r h e a d a t h i g h d a t arates. The FIFO mode increases performance by providingtwo internal 16-byte FIFOs (one transmit and one receive)to buffer data and reduce the number of interrupts issuedto the CPU.Other features of the 16550 include:P r o g r a m m a b l e b a u d r a t e , c h a r a c t e r l e n g t h , p a r i t y ,and number of stop bitsA u t o m a t i c a d d i t i o n a n d r e m o v a l o f s t a r t , s t o p , a n dparity bitsI n d e p e n d e n t a n d p r i o r i t i z e d t r a n s m i t , r e c e i v e a n dstatus interruptsTransmitter clock output to drive receiver logicExternal receiver clock inputThe following pages provide a brief summary of thei n t e r n a l r e g i s t e r s a v a i l a b l e w i t h i n t h e 1 6 5 5 0 A C E . T h eregisters are addressed as shown in figure 2 below.+---------------+-----------------------------------+| DLAB A2 A1 A0 | REGISTER DESCRIPTION |+---------------+-----------------------------------+| 0 0 0 0 | Receive buffer (read) || | Transmit holding register (write) || 0 0 0 1 | Interrupt enable || x 0 1 0 | Interrupt identification (read) || | FIFO control (write) || x 0 1 1 | Line control || x 1 0 0 | MODEM control || x 1 0 1 | Line status || x 1 1 0 | MODEM status || x 1 1 1 | Scratch || 1 0 0 0 | Divisor latch (least significant) || 1 0 0 1 | Divisor latch (most significant) |+---------------+-----------------------------------+Figure 2. Internal register map for 16550 ACE. DLAB isaccessed through the Line Control Register.iii