Z80189 Datasheet, PDF (70/107 Pages) Zilog, Inc. – GENERAL-PURPOSE EMBEDDED CONTROLLERS

Zilog
PRELIMINARY
Z80189/Z8L189
GENERAL-PURPOSE EMBEDDED CONTROLLERS
DOUBLE BUFFERING FOR THE TRANSMITTER IN 16450 MODE (Continued)
Host Write
Empty/Full
Host & MPU THRE = 1 0
16450
THR
Register
Empty/Full
(MPU TEMT) TSRE = _{1 0}
THR to TSR
delay
transfer
Byte Transfer if:
- THRE=0; and
- TSRE = 1; and
- Character delay timer is timed out.
TSR
Transmit
Shift Reg.
Emulation
Note: Timer reloads and counts down
whenever data is transferred from THR to TSR.
Added TSR Buffer for the
transmit data
Host TEMT = 1 if - THRE = 1 and
- TSRE = 1 and
- Emulation delay timer is timed out
Note: MPU sees TSR bit in the LSR Register as TEMT bit
Figure 79. TEMT Emulation Logic Implementation
Z80189 MIMIC DMA Consideration
Z80189 MIMIC Design Hint
Since the /HRXRDY and /HTXRDY is removed in the Z189,
the MIMIC DMA feature found on the Z182 is not available
on the Z189.
The MIMIC output drive capability has been increased to
16 mA on the Z189. This may eliminate the need for
buffering to the PC Bus.
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DS971890301